In this paper, we report on the magnetism and the thermomagnetic power generation performance of a first-order phase transition material Mn1.2Fe0.8P0.4Si0.6,which can be used for thermomagnetic power generation that turns heat directly into electricity. The compound is synthesized by using the high-energy ball milling and solid state reaction method. Magnetic measurements show that the compound undergoes a ferromagnetic-to-paramagnetic first-order phase transition at 337 K, accompanied by a giant magnetization change. According to this feature of the material, we design a demonstration device for thermomagnetic power generation, and study the electric current generated by heat induced phase transition. The current increases with the increase of the heat-flow temperature and the mass of material. This study shows that the Mn1.2Fe0.8P0.4Si0.6 compound possesses the high performance of thermomagnetic power generation.