A recent research hot spot, the sliding window decoding (SWD) of spatially coupled low density parity check (SC-LDPC) codes has the advantages of low decoding latency, low complexity, and small memory requirements. But at present, most of the current research work is focused on Gaussian channels. Over the Rayleigh fading channel, an improved approach to extending the size of the decoding window based on the channel state information (CSI) is proposed, and the CSI is obtained by using the received signal-to-noise ratio (SNR). During the decoding process, if the average received SNR of the current window is less than the preset threshold, the decoding window is extended and then the iteration is performed again. The above process is repeated until the average received SNR of the current window is larger than the preset threshold or the window size is extended to its maximum value, and finally decoding is performed based on the extended window. Simulation results show that the SWD of SC-LDPC codes has a better performance over Rayleigh fading channels, and the performance of the proposed algorithm is significantly better than that of the traditional SWD algorithm.