Abstract: This paper aims at discussing the relationship between body length and body weight of Schizothorax biddulphi, to provide theoretical support for the rational utilization and protection of S. biddulphi. Based on the survey data of the Tarim River Basin in May 2018, we collected the body length and body weight data in the laboratory. Using forecast regressions method to fit expression of body length-weight power function, relative fatness of S. biddulphi and their impact factors were analyzed. The results were as follows:the female groups were less than male groups in body length and body weight, while the body length locus in the two populations were in fitted normal distribution, and there's no significant difference between the two groups;females were higher than males, and there's a significant difference between them;there was a significant correlation between body length, sex and condition factor(P<0.05), while body length-weight equation of females could be described by the equations of W=0.000 023×L^{2.866 8}(r=0.976 8), and males could be described by the equations of W=0.000 049×L^{2.701 3} (r=0.952 9).