Calcium sulphoaluminate was prepared with chemical reagents in this paper.The formation mechanism of calcium sulphoaluminate and effect of CuO on the formation mechanism of calcium sulphoaluminate were investigated by the chemical analysis,X-ray diffraction(XRD),and differential scanning calorimetry(DSC).The results show that there are three ways in the formation of calcium sulphoaluminate.CuO can promote the decomposition of calcium carbonate and decrease the formation temperature of calcium sulphoaluminate(C4A3S).When the burning temperature is below 1000℃,the addition of CuO can promote the formation of calcium sulphoaluminate,while CuO can not favor the formation of calcium sulphoaluminate above 1000℃.