In order to accurately estimate the root biomass and improve the nitrogen accumulation of maize under drip irrigation with full biodegradable film in the Yellow Diversion Irrigation Zone of Ningxia.Using Ningji198(NJ198)and Tianci19(TC19)as experimental materials，root scanner was used to obtain high definition images of maize root system. The vertical distribution of maize root index and biomass under different nitrogen application were analyzed by root image processing system.Root diameter(D) and root length(H) were used to construct root biomass(W) model.The coefficient of determination(R2)， average absolute error(MAE)，standard error(SEE) and average error(ME) of the evaluation index of simulation equation and goodness of fit were evaluated synthetically.The results showed that the root biomass of maize was concentrated in 0～30 cm soil layer，the parameter estimation by nonlinear regression model and the combination variable(D2H) as independent variable significantly improved the accuracy of maize root biomass model，the determination coefficient was 0.94 and 0.86，respectively，and the residual analysis showed that the model had heteroscedasticity.After eliminating heteroscedasticity using logarithmic transformation，the power function model which was constructed by the combined variable(D2H) was the optimal model，the R2 of NJ198 and TC19 was the greatest，which was 0.97 and 0.96，respectively.In order to eliminate the error between different varieties，the data of two varieties in 2020 were fitted，and the optimal root biomass model obtained was:W=3.52(D2H)0.69，R2 was 0.89.The results of model verification showed that the correlation coefficient between root biomass estimation and measured value was 0.92，with MAE，SEE and ME of 0.11，0.13 and -0.09 kg，respectively.It indicated that the model can better simulate the root morphology indicators and biomass distribution dynamics of maize under drip irrigation with full biodegradable film in Ningxia，which can be used as a reference for estimating crop root biomass.