According to the current existing 2 dimensional (2D) and 3 dimensional (3D) spray model, because the coating uniformity still appears insufficient when solving the spray gun path combination optimization planning, it was proposed of a new coating growth rate model that considering the height of spray from spray gun. The model was made with two cases that boundary was parallel and unparallel as the research object commonly appeared in the path combination optimization, and based on the good thickness uniformity principle when the spray gun trajectory was a pathway of parallelparallel (PAPA) in the public side of the patch. Respectively, spray rate revise method, and variable distance and variable speed rate method were adopted to improve the uniformity of spray. Finally, a practical application example and simulation proves the validity of the model.