Abstract: The intelligent sorting system has been widely applied in large-scale pig farming. Some functions can also be realized, including slaughter weight uniformity, the labor saving of manual grouping, and the minimum stress responses of the pigs. In this study, a systematic evaluation was implemented to explore the effects of the intelligent sorting system on both individual behavior and production performance of the fattening pigs. Conventional small-group feeding was also compared with the large-group feeding. Two independent but complementary experiments were carried out on the behavior and production. In the behavior experiment, two treatments were established: a control group with conventional small-group feeding (6 pigs per pen, 4 pens in total) and an experimental group with the intelligent sorting system (60 pigs per pen, 1 pen). Specifically, via the cameras pre-installed above the pens, 24-hour continuous behavioral videos of the pigs were recorded on days 3, 35, and 75 of the experiment. Continuous manual observation and video playback were combined to analyze the frequency, duration, and spatial distribution of the feeding, drinking, defecating, urinating, and fighting behaviors. The behavioral data were then processed into the average group per pig, thus allowing for the comparison over the experimental treatments. In the production performance experiment, the control group consisted of 7 pigs per pen in 8 pens, while the experimental group shared the 63 pigs in a single pen under the Intelligent Sorting System. The initial weight, final weight, and feed intake of the pigs were recorded in the experimental period. The average daily feed intake (ADFI), average daily gain (ADG), feed conversion ratio (FCR), and slaughter weight uniformity were calculated to evaluate the influence of the intelligent sorting system on the growth performance. In terms of the behavior, the feeding duration of the experimental group decreased by 45.1%, compared with the control group. As such, the high feeding efficiency was then obtained to substantially reduce the redundant feeding behaviors. Fighting behavior, a key indicator of social stress, was also greatly reduced: The fighting duration decreased by 75.1% and fighting frequency by 68.0%, compared with the control group. Aggressive competition was effectively mitigated for the group's social stability. At the same time, the proportion of defecation and urination on the slatted floors decreased by 16.4% and 24.9%, respectively, in the experimental group. The behavioral frequencies per square meter of the slatted floor increased by 7.1 and 13.9 events, respectively. The pigs had an excellent preference for the slatted floor excretion. The excretory behaviors were more concentrated per unit area. The low relative proportion of the slatted area highlighted the need for further optimization of the functional area allocation in pen design. In terms of production performance, the average daily feed intake was higher in the experimental group, whereas the feed conversion ratio decreased by 10.1%, compared with the control group. Furthermore, the slaughter weight uniformity was improved by 18.8 percentage points, indicating that the growth variability was reduced within the group. The individual growth efficiency greatly contributed to more uniform market-ready pigs. In conclusion, the intelligent sorting system improved both behavioral efficiency and production performance of the fattening pigs. The stress behaviors (such as fighting) were also reduced due to the high feeding efficiency and slaughter weight uniformity. The welfare-oriented precision was supported in pig farming practices. Modern technology can offer a feasible pathway toward sustainable, efficient, and animal-friendly production. Future studies should focus on the spatial layout of the functional areas in the system. Its effectiveness can be improved to validate the long-term impact on different housing and livestock management.