PC–B type belt driving test bench was improved and modified into a test bench for cutting weed by modifying the driving wheel of the main motor into the cutting and the holding device and installing a pressure sensor which is more accurate than the original one. Humilis, Setaria and goose grass were cut to determine the influence of diameter and moisture content of weed, rotational speeds of motor and cutting angle on cutting resistance. The result suggests that cutting resistance was inversely proportional to the square of the rotational speed and the square of the cutting angle, and proportional to the square of the diameter of weed. Moisture content with different weeds showed different influence on cutting resistance. In contrast to goose grass, cutting resistances for Humilis and Setaria were inversely proportional to the moisture content. Single-factor test showed that a maximum strength of 11.06 N was achieved when the diameter of Humilis was 3.5–4.5 mm, and the moisture content of Humilis was 33.54% (achieved after 10 h drying). Orthogonal test on Humilis showed the cutting resistance was mostly influence by the diameter of weed, followed by the moisture content of weed, the cutting angle and the rotational speed of the motor. Data analysis using Spss showed that the best cutting condition was moisture content of weed being 48.53%, diameter of weed being 3.5–4.5 mm, cutting angle being 60° and the motor rotational speed being 1.2 times larger than the lowest speed.