Based on the family investment model, a study was made to test if psychological suzhi and its dimensions mediate between the family socioeconomic status (SES) of middle school students and their class peer status. The participants, 1801 students from the first grade of junior middle school to the third grade of senior middle school, were asked to complete the questionnaires which measured their psychological suzhi as well as SES and peer status. Significant positive correlations were found to exist between SES and peer status (r= 0.10, p < 0.01), SES and psychological suzhi (r=0.15, p < 0.01), and psychological suzhi and peer status (r=0.20, p < 0.01). The psychological suzhi was found like a mediator between SES and peer status, its mediating effect being 0.03 (95% CI: [0.02, 0.04]). An analysis of multiple intermediary effects on the three dimensions of psychological suzhi showed that only the adaptability dimension played a significant mediating role in the process of SES influence on peer status, the mediating effect being 0.04 (95% CI: [0.03, 0.06]), that is to say, good family SES promotes higher peer status, mainly through its positive impact on the adaptability of adolescents. This finding has deepened, to a certain extent, the study of family investment model and improved the researchers' understanding of the role and function of psychological suzhi.