In order to fully utilize crayfish shell, fermented crayfish paste added with different amounts of crayfish shell powder (0%, 20%, and 40%) was evaluated at different fermentation times for free amino acids, taste nucleotides, organic acids and sensory quality. The relative taste activity value (RTAV) was calculated to determine major taste contributors. The results showed that fermentation time had little effect on the total free amino acids (TFAAs) content of fermented crayfish paste with 0 and 20% crayfish shell powder. Fermented crayfish paste with 20% crayfish shell powder had a more obvious umami taste. The TFAAs content of fermented crayfish paste with 20% crayfish shell powder changed mainly in the early period of fermentation, decreasing significantly, and addition of 20% crayfish shell powder inhibited the bitterness of crayfish paste more significantly. Based on RTAV and variable importance in projection (VIP) scores, potential differential compounds affecting the taste were selected, and the taste substances Ile, GMP, Ala, Val, Leu, IMP, Glu, Asp, Cys, and His played a dominant role in the formation of the taste of crayfish paste. By combining the above results with sensory analysis, we concluded that addition of crayfish shell powder had a significant effect on the flavor of fermented crayfish paste. This study provides a theoretical basis for understanding the effect of addition of crayfish shell powder on the flavor of fermented crayfish paste.