A drilling rig fixing method of portable drilling machine belongs to the technical field of mining engineering and comprises the steps: step 1, water is mixed with a leak-stopping agent; step 2, a base tray fixing platform is constructed on the surface of a rock mass with the mixture of water and leak-stopping agent; step 3, expansion screw holes are drilled on the base tray fixing platform and the lower part of the rock mass; step 4, a base tray is fixed on the base tray fixing platform by using first expansion screws; the base tray, the base tray fixing platform and the rock mass are fixed together by the first expansion screws; and step 5, a drilling rig is fixed on the base tray by second expansion screws, and the drilling rig, the base tray, the base tray fixing platform and the rock mass are fixed together by using the second expansion screws. The drilling rig and the expansion screws during working directly contact with the base tray, but not rock walls; the drilling rig is compact to fix and does not separate from the rock walls to result in the violent shaking of the drilling rig; the rejection rate of drilling holes is reduced and the drilling efficiency is improved while the cost is reduced.