The work aims to research the unevenness of soybean protein spraying under different spraying parameters, so as to improve heat sealing effects of vegetable composite paper. The spraying samples were collected by the camera, and the images of vegetable parchment after spraying were processed and analyzed by Matlab programming. The area ratio of soybean protein coating was obtained. Finally, the influence of different spraying parameters on soybean protein coating area ratio was analyzed by Origin. When hydraulic pressure or air pressure was 120~220 Pa, the area ratio of soybean protein coating increased first and then decreased with the change of hydraulic pressure or air pressure. When the flow rate was 35-60 mL/min, the area ratio of soybean protein coating increased first and then leveled up, and finally decreased with the change of flow rate. At different transverse test points of the same parameter, the area ratio of soybean protein coating was relatively small at both ends of spraying area and relatively large in the middle of spraying area. Hydraulic pressure, air pressure and flow rate have a great impact on the soybean protein liquid spraying unevenness, and under a single factor, when the hydraulic pressure is 160 Pa, air pressure is 180 Pa or flow rate is 50 mL/min, the spraying effect is better.