The invention discloses a method of evaluating particle emission harm of a diesel engine. The method comprises the steps of selecting evaluation indexes of different particle harm, establishing a hierarchical structure model, constructing a judgment matrix according to expert knowledge, calculating weighted values, constructing a principal component analysis model and establishing a correlation coefficient matrix, using the correlation coefficient matrix to solve characteristic values and principle component distributions, determining principle components, solving principal component load and an expression, and establishing comprehensive scoring function H for particle emission harms. Through the comprehensive scoring function H, consideration is made to harm to different human systems by different particle sizes of particles.