According to the shape of 3-arcs blade the distribution function equations on 3-arcs blade surface were deduced and the hydraulic characteristics on blade surface were analyzed. Based on the establishment of relative velocity and pressure equations, the step change equations of relative velocity and pressure on blade surface were also deduced on connected line which was formed by the intersection of two cambered surfaces, and the reason and the relationships between control parameters were revealed. The step change value of relative velocity is equal to diameter difference of two intersect arc cylinders. The step change value of pressure is concerned with the position coordinates of initial origin of two intersect arc cylinders. Calculation example confirmed that the step changes of relative velocity and pressure will appear on intersection of two cambered surface.