The invention discloses a method for determining the drill hole effective extracting radius by testing the coal seam gas content and gas pressure jointly. According to the method, the construction sequential order is reasonably arranged and controlled, construction of a pressure measurement drill hole, an extracting drill hole and a gas content testing drill hole and testing work of the gas pressure and the gas content are constructed. Whether the coal seam gas residual content in the extracted gas content testing drill hole is smaller than 8 m<3>/t or is smaller than 30% of the extracting drill hole gas content serves as the criterion, and the drill hole extracting gas effective radius R1 is determined. According to the mutual relation of the gas pressure and the gas content in the Langmuir equation, whether the gas pressure Pc in the gas pressure testing drill hole after extracting is smaller than 0.7P/1+0.3bp (P is the gas pressure before extracting, and b is the adsorption constant) or is smaller than 0.74 mpa serves as the criterion, and the drill hole extracting gas effective radius R2 is determined. The drill hole effective extracting radius R of the joint testing method is the larger one in the R1 and the R2, and R is equal to max {r1and R2}.