Determination method for effective extraction radius of drilled holes

The invention provides a determination method for the effective extraction radius of drilled holes. The determination method comprises the steps that multiple sets of drilled holes are formed in a to-be-measured coal seam area, each set of drilled holes comprises a flow observation hole and multiple auxiliary extraction holes, and the centers of the flow observation hole and the multiple auxiliaryextraction holes in each set of drilled holes are arranged at equal distance; the flow observation holes and the auxiliary extraction holes are connected with a gas extraction device; the gas extraction quantity of each day is determined according to parameters, monitored by the gas extraction device, of the flow observation holes; and when the total gas extraction quantity accumulated in day N-1is smaller than the total quantity of gas needing to be extracted in the to-be-measured coal seam area, and when the total gas extraction quantity accumulated in day N is larger than or equal to thetotal quantity of gas needi