The work of low-head water turbine mainly relies on the large flow rate, but the larger flow at different positions of the flow channel are easy to cause different hydraulic loss, and they may also have a poor stability. The paper based on a typical case of low-head water turbine unit over the Yellow River, according to the efficiency of the low-head water turbine and the hydraulic loss theory, and according to the real machine guide vane and the surface shape of turbine vane, and when a fixed vane turning, change the guide vane outlet angle and calculate the computing velocity and energy characteristics, then the unit was found with the high est efficiency between the 200 m3 / s - 250 m3 / s, and then we put forward the concept of conditions interval optimization from the angle of theory. Do corresponding numerical simulation on its working conditions and the real machine test under the same working condition, the test results consistent with theoretical calculation. In combination with theoretical calculation and the real machine test conclusion, and on the basis of the conclusion of low-head water turbine to make condition optimization and through the actual operation to achieve a certain effect, which provide a solution for the economical and safe operation of the low-head water turbine.