Lightweight stainless steel has widely potential applications in many fields, such as automobile, ship, submarine manufacturing and aerospace. The properties of lightweight stainless steel are significantly affected by the precipitating behaviour of second phase particles. In this paper, the precipitating behaviour was investigated by XRD, DSC in the process of cooling and thermodynamic calculation combining the Miedema's and Chou's model. The XRD results indicate that there are five types of phases in lightweight Fe-Mn-Al-C-N stainless steel: ferrite, FeAl, AlMn, AlN and Mn4N. The DSC results show that the precipitating temperature of FeAl, Mn4N is 1260℃, 1031℃, respectively, corresponding to the thermodynamic calculation. Besides, The DSC measurement reflects the precipitating temperature of AlMn and austenite is 934℃ and 600℃.