Simultaneous reactions between solids and gases are very important in the chemical and metallurgical processes. In the modeling, the chemical reaction and diffusion of gases must be considered. Therefore, a set of coupled partial differential equations is found. When the kinetic is a function of solid concentration, there is not any analytical solution for these equations. Therefore, numerical or approximate solutions have been used. In this paper a new approximate method has been developed for solution of two gases-one solid reaction equations. This technique offers some new mathematical expressions for rapid calculations. The results of this method are compared with the existing solutions. The quantized solution shows a better accuracy than other approximate method.