The effects of latex powder （FX）， cellulose ether （HM） and starch ether （KH） on rheological properties， working properties， anti-dispersant properties and mechanical properties of underwater 3D printing building mortar （3DP-BM） were studied. The results show that 3DP-BM cannot be printed underwater without FX or HM， or with too much KH. Mixed with FX， HM and KH together， 3DP-BM has good working performance， appropriate mechanical strength and underwater anti-dispersion performance. When the content of FX， HM and KH is 0.500%， 0.100% and 0.025% respectively， 3DP-BM has suitable operational time， good underwater anti-dispersion property， and high underwater strength and underwater stacking height.