The invention provides an angular trimmer for a grinding wheel of a grinding machine, which comprises a bottom plate, a diamond stylus, a sliding plate, a slider, a circular gear, a rotary rod and an adjusting supporting rod. The sliding plate is provided with a protrusion which is provided with a slot extending through the whole protrusion, the slider is provided with a groove, a strip toothed boss with a toothed opening is arranged at the bottom of the groove, the groove of the slider is slidably fixed with the protrusion of the sliding plate, and the groove is slidably fixed with the toothed boss. The diamond stylus is perpendicularly fixed to one face of the slider, one side of the sliding plate is movably and fixedly connected with the side of the bottom plate through the adjusting supporting rod, an adjusting gasket is arranged on a slide on one side of the sliding plate and fixed by a screw, and connecting blocks with symmetrical through holes are fixedly arranged on two sides of the sliding plate. The rotary rod penetrates through the through holes to be movably fixed with the connecting blocks, the circular gear is fixedly arranged on the rotary rod, the sliding plate is provided with an open slot, and the circular gear is meshed with the toothed boss through the open slot. The position of the slider and the height of the sliding plate are adjusted to fit angular adjustment of large-diameter grinding wheels.