Abstract: The application of a comprehensive thermal analyzer Diamond TG/DTA in the research of magnetic material is introduced. Under the action of magnetic field, thermogravimetric curves(TG) of the samples were obtained. From the analysis of the TG curve of the magnetic phase transition of sample and the cause of the Curie temperature change, it is seen that positioning of the replaced Co element on the rare earth iron compound sample and the interaction between the elements have great impact on the Curie temperature. As a measuring method for Curie temperature,it expands the field of application and research for Diamond TG/DTA.