Aiming at the problem that the sequence of operation in the processing of complex parts directly affects the processing cost, an improved harmony search algorithm with the lowest processing cost as the optimization goal is proposed. The constraint relationship between the operation is represented by a process priority diagram. Then use the topological sorting method on the graph to generate the initial sequence as the initial harmony of the harmony memory. The crossover operator is introduced to ensure the feasibility of the new generation of harmony, and the local search method is used to change the machine and tool resources available for the operation to avoid falling into the local optimum. Experimental results show that the improved harmony search method can effectively solve the cost optimization problem of step sequencing.