The definition of spatial cylindrical surfaces is extended, amplifying on the definition of corresponding planar curves. Fitting of the spatial cylindrical surface using genetic algorithm is suggested in this paper. Taking the fitting of cylinder surface for example, the principle and method of spatial cylindrical surface fitting based on genetic algorithm is described. Express parameters are to be identified in this method. Non-independent parameters are constrained. Objective function is built based on least squares method. Optimization is achieved using GA. The effectiveness and advantage in fitting precision of the method proposed in this paper is testified using an engineering example.