The utility model discloses a grass trimmer and aims to solve the problem of lower efficiency of a mower in the prior art. The grass trimmer comprises a rack, a power device and a transmission device and also comprises two cutting devices which are arranged in parallel along the advancing direction of the grass trimmer; the transmission device comprises a first horizontal transmission shaft in belt transmission with the power device, an oblique transmission shaft in bevel gear transmission with the first horizontal transmission shaft, and a second horizontal transmission shaft in bevel gear transmission with the two cutting devices; a sleeve comprises a first horizontal sleeve integrally fixed and sleeved with the first horizontal transmission shaft, a second horizontal sleeve sleeved on the first horizontal transmission shaft and a U-shaped sleeve for connecting the second horizontal sleeve and the first horizontal sleeve; one side of the U-shaped sleeve is sleeved with an oblique transmission shaft; the U-shaped sleeve and the second horizontal sleeve are in square arrangement. The grass trimmer is simple, practical and efficient.