Abstract: To find the rule of structural progressing of phenol-urea-formaldehyde (PUF) resin prepared under alkaline condition and to provide theoretical basis for PUF preparation, quantification of main functiongroups and identification of different linkages formed in PUF prepolymers were analyzed by 13CNMR spectroscopy when phenol, formaldehyde and urea were charged by several times during the preparation of PUF. Results showed that PUF prepolymers obtained by different charging methods showed similar chemical structure with almost same type of linkage but showed difference in structural constitution. Under definite materials' ratio in this experiment, the final reaction progresses of synthesizing PUF resins were almost similar. The charging of formaldehyde by several times could decrease the formation of ether and was in favor of simplifying the reaction. Results of thermo-mechanical analysis (TMA) exhibited that curing performance of PUF prepolymers were not much affected by different charging methods.