In this paper,DTA-TG and TEM are used to investigate dolomite containing phosphorus. The investigations suggest that the thermal decomposition of dolomite containing a little bit of phosphorus powder has only one reaction while that of dolomite has two reactions, and the final temperature of the reaction reduces by about 18°C. The oxidation reaction of the phosphorus in dolomite begins at about 500°C, which is 140°C higher than that of the oxidation reaction of phosphorus in standard atmosphere condition. Round-bubble-shape structure gradually appears on the surface of the dolomite sample when observed using TEM. Furthermore, the number and size of this structure increased with the rising of the temperature. Finally, the round-bubble-shape structure breaks to small hollows, showing as teared-shape, and forms a series of protruding and intensive larger hollows and spherical shape. Therefore, the temperature of thermal decomposition of thermal decomposition of dolomite is decreased and the components of thermal decomposition products of dolomite containing phosphorus are almost the same as that of dolomite.