The thermodynamic calculation for deposition reaction was performed by com- puter program Solgasmix- PV,the calculation results show that the deposition of Cr and Si onto iron- base alloys is possible by the use of a ternary activator(e.g.Na F+Na Cl+Al F3) ,a promis- ing coating can be deposited by a cementation powder mixture of Cr and Si in proportation of 1 2 / 1 .