Because of the position instability and atmospheric turbulence are two of the major influences on high altitude platforms (HAPs) optical links, the method to improve the performance of HAPs optical links using spatial diversity is presented. The expressions of HAPs optical links bit error rates (BER) for multiple-input multiple-output (MIMO) scheme and cooperative diversity scheme are obtained with on off keying (OOK) modulation system. And the optimum place for the relay platform is shown. The simulation results show that the improvement of cooperative diversity and optical MIMO on HAPs optical communications may be restricted by tracking error. The BER performance of MIMO optical links based on transmit laser selection is the best. Compared with MIMO optical links based on repetition coding, cooperative diversity is suited to optical communication links with bigger pointing error. The optimum place of the relay platform for HAPs optical links with cooperative diversity is independent on relay strategy and pointing error. The cooperative diversity scheme is superior to the HAPs MIMO optical links with repetition coding when the place of the relay platform is optimum.