The light scintillating caused by atmospheric turbulence, absorption and scattering can increase the energy attenuation of the laser beam and decrease the signal to noise ratio(SNR). Diversity reception technology can overcome this effect, effectively. Using on off keying (OOK) modulated, free space optical communication (FSO) system with spatial diversity based on the K-distributed model is established. The error performances among three linear combining technologies as maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SC) for different channel parameters and different detectors are analysed. The simulation results show that the performance of the system by MRC is the best, followed by EGC, and SC combining is poor. Spatial diversity has strong ability to improve the performance and resistance to atmospheric channel decline.