A modulation scheme of 6-PolSK for atmospheric laser communication is proposed. Theoretical analysis result demonstrates that the states of polarization (SOPs) and degree of polarization (DOP) of light wave can be well maintained after long distance propagation in the atmospheric channel with different turbulence models. Simulation results show that the transmission performance and the bandwidth efficiency are improved considerably. 6-PolSK modulation is an attractive approach to meet the criteria about data rate and bandwidth efficiency of the atmospheric laser communication system.