There are many welding fixture layout design problems of flexible parts in body-in-white assembly process, which directly cause body assemble variation.The fixture layout design quality is mainly influenced by the position and quantity of fixture locators and clamps.A general analysis model of flexible assembles deformation caused by fixture is set up based on "N-2-1" locating principle, in which the locator and clamper are treated as the same fixture layout elements.An analysis model for the flexible part deformation in fixturing is set up in order to obtain the optimization object function and constraints accordingly.The final fixture element layout could be obtained through global optimal research by using improved genetic algorithm, which effectively decreases fixture elements layout influence on flexible assembles deformation.