In order to solve the mixed-model sequencing problem of stochastic assembly line, the influence of stochastic operation time on scheduling optimization goal is analyzed, and a concept of effective mathematical expectation, describing the station's idle time and overload time, is proposed. Under stochastic operation time, an optimization model is built by taking the station load balance as the evaluating indicator. And then, the elitist strategy and variable neighborhood search are added in the standard fireworks algorithm to design a improved fireworks algorithm to solve this optimization model. Test examples and production instances are given to ill ustrate the effectiveness of the proposed model and algorithm.