Based on the theoretical analysis and model experiment, the behavior of flow in front of the sluice gate, flow diversion ratio of a low head sluice built in the curved channel and its factors were analyzed, calculations of flow diversion ratio coefficient were discussed. The results show that due to the influence of sluice on the flow, the transverse and longitudinal gradients of the water surface decrease remarkably, the transverse distribution of the depth-averaged longitudinal velocity tends to be nearly uniform. The impact of the total flow and the angle between sluice axis and inlet plane of curved channel on flow diversion ratio of a low head sluice is small. Discharge capacity of the gate-hole near convex bank is small, those of other gate-holes are much uniform. Flow diversion ratio coefficients by calculation were satisfactory. These results are very important for the selection, location, design, security and economy of sluices.