Water content has important influences on the compression strength of mortar material. It is necessary to consider these influences when evaluate performances of mortar structures after flood soaking. This paper carried out experiments to explore the rule of water content’s effects on the compression strength of mortar. The results showed that 6 hours after the mortar in the soaking water content close to saturation, moisture content about 14%, after 6 hours the water content change little. Compression strength decreases rapidly after the mortar soaked. Finally, the mortar compression strength formula considering the effects of water content is regressed.