The invention discloses a method for gas extraction on the weak surrounding rock fully mechanized caving face, and the method is suitable for a mine where the gas concentration of the caving face is liable to overrun in the top coal caving process of the thick coal seam weak surrounding rock fully mechanized caving face. A vertical pipe is constructed to the upper portion of a coal seam through a pneumatic anchor rod driller at the upper corner of an air return roadway of the fully mechanized caving face, the gas extraction vertical pipe is arranged in the coal seam, a large amount of gas generated in the top coal caving operation process is extracted timely, and accordingly the gas concentration of the fully mechanized caving face is reduced; the problem that under the condition of weak surrounding rock, hole-forming fails when oblique-crossing layer penetrating pre-extracting drilling is constructed on the upper portion of a goaf in the air return roadway is solved; the large amount of gas rushing out of fully mechanized caving face coal masses in the top coal caving operation process can be extracted, so that the gas concentration of the caving surface and the upper corner is reduced effectively; and meanwhile within the period of caving surface advancing, the gas of the goaf behind the caving face can be further extracted, the emission amount of the gas in the goaf is reduced, and the gas concentration of the caving surface is reduced. The structure is simple, mounting is convenient, operation is easy and convenient, and practicability is high.