The invention relates to an automatic fish hook. A fish hook main body is made of an elastic steel wire and resembles a torsion spring; an upper retaining ring is fixed in the middle of a ring at the upper part of the fish hook main body, and a lower left retaining ring and a lower right retaining ring are respectively fixed at the left side and the right side of the lower part of the fish hook main body. Both feet of the fish hook main body can point to the outside when the fish hook main body freely springs out, can point to the inside and can naturally fold when the fish hook main body correspondingly shrinks. An opening needle sequentially penetrates through a middle hole of the upper retaining ring, and a hole of the lower left retaining ring and a hole of the lower right retaining ring when the fish hook main body is in a compression folded state so as to fix the compression folded state of the fish hook main body, fixedly connect a hanging line with the ring at the upper part of the fish hook main body and enable a buffer line in a loose state. The fish hook main body is pulled downwards by a hooked fish when the hanging line is fixed, and the buffer line is straightened to ensure the opening needle to separate from the holes of the lower left retaining ring and the lower right retaining ring so as to reliably stretch the fish hook main body in time and clamp the hooked fish in time.