To apply the orthogonal design to the optimization of the coal-seam injection technical parameters' combination is a better method that realizes the best effect of injection for the coal-seam with steady geological conditions. But with this method, its effect cannot definitely satisfy the injection engineering requirement for the coal-seam with changing geological conditions. For this reason, in view of the coal-seam with unsteady geological factors and the characteristic that the geological factors have both qualitative and quantitative variables, one method that applies the quantity theory and orthogonal design to determine the optimal combination of injection technical parameters is raised and the engineering experimental study has been made. The experiments show that this method can save the quantity of injection experiment engineering and are approaching to the actual engineering requirement.