Abstract: According to the hydraulic similarity theory and combined the design of a rotation flow girt chamber, a solid-liquid separation equipment model was developed with four factors, which were diameter for outlet, long for outlet pipe, water head, and diameter for inlet, influencing the efficiency of grit removal. By applying the single factor and orthogonal experiments, the importance and the optimal condition of four factors under different sand particle size conditions were studied. Results showed that the increasing water head improved the efficiency of grit removal, but large water head reduced the efficiency. Small diameters of the inlet improved the efficiency of grit removal, while large diameters of the outlet improved the efficiency of grit removal. In addition, long outlet pipe also improved the efficiency of grit removal. The optimal conditions of four factors for the 100 mesh sand were as follows: 30 mm diameter for the outlet, 45 cm long for the outlet pipe, 35 cm water head, 40 mm diameter for the inlet. The optimal conditions of fours factors for 30 mesh sand were as follows: 60 cm water head, 40 mm diameter for the inlet, 30 mm diameter for the outlet, and 30 cm long for the outlet pipe. Under the optimal condition of 4 factors, the efficiency of grit removal in 100 mesh sand was 82.14%, and 83.55% for 130 mesh sand. Our findings may provide valuable references for the design of grit chamber for the small-scale sewage treatment.