For the high machining precision and various complicated constraints, process planning of cylinder block always receives lots of attention from industry and academic fields. FMEs (feature machining elements, FMEs) is proposed in this paper, which subdivided from design features and had a close correlation with machining methods according to machining accuracies and manufacturing resources. Therefore, the problem of process planning could be represented by an optimal sequencing and balancing of those FMEs. After analysis of constraints of features and FMEs, an optimal objective is established during a certain stage, and a process planning is generated and optimized by using an improved genetic simulated annealing algorithm (GSA). Finally, a case of cylinder block reveals that the proposed method is feasible and efficient.