Experimental investigations on impinging diffusion flames mixing with inert gas were conducted. The combustion results and temperature measurements show that the non-reactive gas might dilute the local fuel concentration in the diffusion process. The shape of the column flame was symmetrical due to the flame stretch force. The results showed that a conical flame was changed by the addition of inert gas to the pure methane fuel. The weakening of the stretch boundary enhanced the mixing rate between the fuel and oxidizer, which would improve the fluctuation phenomenon. The impinging flame became shorter and bluer so the combustor size can be reduced. Nitrogen gas has the advantage that we can visualize the impinging mechanism with different gases in the impinging flame. The color in the mixing plane becomes blue and transparent. The penetration length is about 8 mm near the impinging point for Re = 145.