Aiming at the problem of fast setting time and poor workability of fast-setting and fast-hardening high belite calcium sulfoaluminate (HB-CSA) cement, the effect of ethylenediamine tetramethylene phosphonic acid (EDTMP) on the setting time, fluidity and mechanical properties of HB-CSA cement was investigated by hydration heat, X-ray diffraction, thermogravimetric and mercuric pressed tests. The mechanism of action of EDTMP in HB-CSA cement was analyzed. The results show that EDTMP can effectively retard the setting time of calcium sulfoaluminate cement and improve the fluidity. When the EDTMP contnet is 1.00% (mass fraction), it can prolong the initial setting time of HB-CSA cement to 62 min and prolong the final setting time of HB-CSA cement to 76 min. EDTMP can inhibit the reaction between anhydrous calcium sulfoaluminate (C₄A₃$$\bar{S}$$) mineral and gypsum phase of HB-CSA cement in order to inhibit the rapid generation of ettringite (AFt), which is an early hydration product of cement, so that HB-CSA cement retarding can be achieved.