Abstract: For open quantum ensembles with Hamiltonian fluctuations composed of a large number of single quantum systems, a two-stage approximate time-optimal control algorithm is proposed in the framework of coherence vectors of density matrices and achieves a high-fidelity state transition of all member systems to a common target state within an approximate minimum control time. According to the parameter distribution rule that characterizes Hamiltonian fluctuations, this algorithm first samples the whole ensemble to obtain a sample system set. Then, based on the obtained sample system set and via the basic gradient method, the fidelity and the control time are optimized in the two stages respectively, and the resulting optimal control law is obtained. Numerical simulation experiments on a two-level open quantum ensemble verify the effectiveness of the proposed algorithm.