Abstract: The wireless channel in satellite mobile communication system is typical fading channel. The channel impairments can be usually described by three fading phenomena, including Rayleigh fading, Rician fading and shadowed Rician fading in different environments. To obtain reliable communications, there is a significant need for method to combat detrimental effects in this wireless fading channel. Recently，the cooperative diversity transmission technique has attracted considerable research attention as it is capable of significantly improving the performance of wireless communication systems. Several cooperation strategies with different relaying techniques, including amplify-and-forward (AF)、decode-and-forward (DF) and CodedCooperation (CC), have been studied in Laneman Sendonaris and Hunter et al.’s seminal paper。In this paper，cooperative diversity technology was considered in the user downlink of the low Earth orbiting (LEO) satellite mobile communication system to reduce the influence of channel fading. The system model was given and the general error probability for decode-and-forward was analyzed,then the system error probability over Rayleigh, Rician and shadowed Rician fading channels in the user downlink were obtained.The simulation results can coincide with the theory analysis. What's more, the results show that the proposed system can outperform the traditional system without the cooperative diversity technology.