The silicon coating was sprayed on titanium substrate by low pressure plasma spraying and the subsequent coating was heat-treated in vacuum. It is found that a titanium silicide coating with the composition changed gradually can be formed through thermal diffusion treatment of silicon coating sprayed by low pressure plasma on titanium substrate. The formed silicide coatings are characterized by optical microscopy, scanning electron microscopy, EPMA analysis and X-ray diffraction (XRD). The forming process of the silicide coating is investigated by examining the relationship between silicide coating thickness and thermal diffusion parameters. The results show that the composition of silicide coating changes gradually from TiSi, at the silicon coating side through TiSi and Ti5Si4, to Ti5Si4, near substrate side. The thickness of such graded silicide coating is determined by temperature and holding time during heat-treatment. The diffusion of silicon into titanium substrate is mainly responsible for the formation of silicide. Moreover, the investigation of oxidation behavior of silicide coating shows that the formation of silicide coating on the titanium substrate can improve the oxidation resistance of titanium.