This paper uses an industry case, dust mask improvement, to illustrate the procedure of function analysis: component model, interac-tion matrix, function tabular form and func-tion analysis diagram, to generate two target disadvantages. Afterwards, one of the target disadvantages, sealing insufficiency of outer layer, is further tackled through the cause ef-fect chain analysis to dig out a deeper cause - pressure is not even. Using the physical con-tradiction to describe the root problem, a sep-aration in space principle is taken to solve the problem with relevant invention principles. It issues in four plausible specific solutions, which are recommended by the industry sponsor, with several other possible solutions.Keywords: Component model, Interaction matrix, Function analysis diagram, Cause effect chain analysis, Physical contradiction.