Research on the relationship of SiN_x film to off-angle color shift on white screen is carried out. The research in this paper fills in the lack of research of correlation between TFT film and off-angle color shift of TFT-LCD, and provides a useful reference for the improvement of similar optical chromaticity defects in other products. Through experimental measurement and software simulation, the influence of the thickness of the silicon nitride film on the color shift coordinates is explored. Experimental results show that the silicon nitride film layer is a key factor affecting the color shift, GI and PVX1 have a greater impact on color shift, while PVX2 has a little impact on color shift,and the thickness of the SiN_x is nonlinearly related to off-angle color shift on white screen. Taking a HADS product for example, the SiN_x film layer includes gate insulating layer (320 nm), 1st passivation insulator layer (100 nm), 2nd passivation insulator layer (200 nm). Based on single-factor experimental and simulation results, comprehensively considering the electrical characteristics and production capacity, the reddish on white screen from the viewing angle is improved effectively when PVX1 140 nm is used as the condition. That means there is no reddish by macroscopic observation and the measured data meets product specifications.