Currently when the domestic concrete pump is pumping, the piston of master cylinder may hit the cylinder or not travel enough displacement; the travelling rules in different conditions have been not found yet. In this paper, an open circuit hydraulic control system is researched by simulation software AMESim, pumping circuit and dividing circuit of the system are modeled and simulated. The simulation results are compared with experimental results to illustrate the accuracy of the modeling. Then the relationship between travelling displacement of the piston and the factors, such as location of trigger port, different diameter of damping u-tube, is analyzed. In the end, a set of reasonable design parameters of the hydraulic system is proposed.