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In this paper, a theoretical model based on the micromechanics method is proposed to analyze the strain distribution and the performance degradation of bronze route Nb3Sn superconducting strand due to thermal strain and external loads. The effect of twisting on the Nb3Sn superconducting strand is considered. The strain distribution in the filament is analyzed by applying the Mori-Tanaka method. The critical parameters characterizing the superconducting properties of Nb3Sn filaments are discussed by using the model proposed by Markiewicz. It is found that twisting of the filaments has a significant effect on the stress-strain distribution. When the pitch length is not large enough compared to the strand diameter, it has a significant effect on the performance degradation. Moreover, the shorter the twist pitch, the higher the degradation of the critical parameters. When the pitch length is much larger than the strand diameter, it has little influence on the performance degradation.