The invention relates to the technical field of radial horizontal drilling, in particular to a flexible shaft fishing tool for radial horizontal drilling. The lower end of an upper connector of the flexible shaft fishing tool is connected with a ball universal joint, and the lower end of the ball universal joint is connected with a lower connector. The ball universal joint is formed by sequentially connecting a plurality of ball nipples, four key grooves are symmetrically formed in the ball end of each ball nipple, four screw holes are symmetrically formed in a ball groove in the other end of each ball nipple, and the four screw holes in the ball groove of each ball nipple are connected with the ball end key grooves of the corresponding ball nipple at the upper end; and every two adjacent ball nipples can be bent and rotated, and the lower end of the lower connector is connected with a fishing barrel body. The flexible shaft fishing tool can successfully fish flexible shafts which fall off, radial drilling construction is not affected after fishing, accident risks are lowered, the labor intensity of operators is reduced, the accident handling period is shortened, and the construction cost is lowered.