Abstract: The quality of cladded products depends on the dilution and reinforcement of the overlay, which are the comprehensive results of cladding parameters. Mathematical models between GTAW cladding parameters of Inconel 625 (including welding current, welding speed and wire feed rate) and the dilution/reinforcement of the overlay were proposed. The models were based on central composite rotatable design, which is a typical design method of response surface methodology (RSM). The effect of process parameters on the dilution and reinforcement were analyzed to optimize the cladding process. Experimental results shows that the wire feed rate has significant effect on the reinforcement while welding current and welding speed have less effect. Welding current has the most significant effect on the dilution while welding speed has the weakest effect. The interaction of welding current and welding speed also have significant effect on the dilution.