The invention discloses a sheet material positioning mechanism and a paint spraying method. The sheet material positioning mechanism is used in a paint spraying assembly line and can make paint quickly and locally sprayed on a sheet material. The sheet material positioning mechanism comprises a pushing assembly and a positioning assembly which are arranged on working tables on the two sides of anassembly line conveying belt, the front end surface of the pushing assembly is a step-like pushing surface gradually moving backward from top to bottom, and a first push-pull device is connected withthe rear end of the pushing assembly, fixed to the corresponding working table and used for driving the pushing assembly to reciprocate in the direction perpendicular to the direction of the assemblyline conveying belt. The front end surface of the positioning assembly is a step-like positioning surface in the shape corresponding to the shape of the pushing surface, and a second push-pull deviceis connected with the rear end of the positioning assembly, fixed to the corresponding table and used for driving the positioning assembly to reciprocate in the direction perpendicular to the direction of the assembly line conveying belt. The pushing assembly is matched with the positioning assembly so as to be used for positioning the stacked sheet materials.