The present invention relates to the technical field of herbicide crystallisation processes, and relates in particular to a dicarfentrazone-ethyl crystalline form C, and a preparation method therefor and a use thereof. The X-ray powder diffraction pattern of the dicarfentrazone-ethyl crystalline form C has characteristic peaks at 2θ diffraction angles of 10.159, 10.658, 13.318, 14.579, 16.096, 18.061, 19.322, 19.68, 20.04, 20.659, 21.281, 23, 24.16, 24.619, 26.101, 26.74, 30.359, 31.018, 32.378, 35.398 and 38.26, wherein the 2θ error range is within ±0.2°. The dicarfentrazone-ethyl crystalline form C has good stability, and has a better control effect on broadleaf weeds and some grassy weeds when in a compound composition with other effective ingredients, the effect being significantly better than crystalline form A.