Abstract: The influence of partial coherence on random seismic responses of long-span spatial structures is studied. The formation algorithm for the pseudo excitation of the multi-support and multidimensional random earthquake considering the partial coherence effect is improved. The property of the partial coherence matrix is investigated, and an algorithm to increase the computation efficiency for the random seismic analysis considering the partial coherence effect is proposed. The coherence matrices in the cases of coherence, partial coherence and incoherence are compared, and the influence of the partial coherence on the random seismic responses of structures is analyzed. The random seismic responses of a large reticulated shell structure of a gymnasium are numerically simulated for different coherence cases. It is found that, for some members near the ground supports, who behave mainly pseudo-statically, their responses are augmented significantly with the partial coherence effect considered. But for the other members far from the ground supports, who behave mainly pseudo-dynamically, their responses are weakened. Therefore, for the long-span spatial structures, the partial coherence effect of the earthquake must be considered in the random seismic response analysis, especially when those members behaving pseudo-statically govern the seismic design of the structures. The proposed techniques about the formation algorithm of the pseudo excitation of earthquake may increase the computation efficiency for the random seismic analysis of the long-span spatial structures.