Abstract: Aerobic composting has been limited by the relatively high pH value of the cow manure compost products. The organic fertilizer quality can be required to reduce nutrient loss. The acid-producing bacteria can be expected to reduce the pH value and nitrogen loss in the cow manure compost. But, its addition can often be regulated during composting. This study aims to explore the effects of the composite lactic acid bacteria agent and anaerobic fermentation pretreatment on the aerobic composting of the cattle manure. The lactic acid bacteria were also isolated and then screened from the fresh cow manure. Four treatments were designed: T1, the material was added with a composite bacterial agent for 4 days before aerobic fermentation; T2, the composite bacterial agent was added, followed by aerobic fermentation with ventilation; T3, sulfuric acid was added, followed by aerobic fermentation with ventilation; T4, sulfuric acid and the composite bacterial agent were added and fully mixed before aerobic composting. The original aerobic composting was used as the control (CK). The results show that the 21 suspected strains of the lactic acid bacteria were isolated from the fresh cow manure. Two target strains were obtained after initial and secondary screenings, based on their rapid growth and strong acid production. These strains were identified as Lactobacillus amylovorus LB31 and Weissella paramesenteroides BY1. The optimal viable cell ratio of the composite bacterial agent was prepared from the two strains of 7:3. The pH value of the material also decreased from 7.67 to 7.38 after anaerobic fermentation pretreatment. The T1 treatment shared a 4.07% reduction in the pH value, compared with the CK. Furthermore, the T1 treatment also exhibited the least carbon and nitrogen loss at the end of the composting, which decreased by 27.53% and 37.50%, respectively. The mass fractions of the available phosphorus and available potassium increased by 14.68% and 10.95%, respectively, whereas the pH value decreased by 0.46. In conclusion, the optimal procedure was obtained to add a 3.0% mass fraction of composite lactic acid bacteria agent into cow manure compost, followed by 4 days of anaerobic fermentation and aerobic composting. The pH value of the compost material and product was significantly reduced due to low nutrient loss during composting. This finding can provide the bacterial strain resources for the application of the lactic acid bacteria in composting. While the theoretical and technical foundations can also offer to combine the anaerobic and aerobic processes for the low pH compost and nutrient loss.