Abstract: Fertilization equipment is one of the most important equipment for the fertigation system in recent year. The performance of fertigation pump directly dominates the quality of irrigation and fertilization. Among them, the proportional fertilization pump can be expected to serve as an advanced fertilization equipment. Specifically, the water pressure can be used as the power source in the most areas without electricity. The fertilizer suction piston is one of the vital hydraulic components to promote the accuracy of fertilizer injection. Taking the suction piston as the study object, the quadratic regression orthogonal combination test was carried out to optimize the major structural parameters, according to the operating principle. The injection flow rate was utilized as the response index. A multiple regression model was established for the response index and factors. The variables included the diameter of the lower end of the suction piston, the width of the discharge groove, and the depth of the discharge groove. The results demonstrated that the actual injection ratio of the proportional fertilization pump was lower than the predicted injection ratio under various differential pressures and injection ratios. The difference between the actual and predicted injection ratio was reduced with an increase in the injection ratio, at the differential pressure of less than 0.15 MPa. It infers that a larger injection ratio was preferred to boost the fertilizer injection accuracy. The greatest factors were determined in the injection flow within the factor level range, including the width of the discharge groove, the depth of the discharge groove, and the diameter of the lower end of the suction piston(P＜0.01). The injection flow rate was significantly influenced by each of the three parameters individually, as well as significantly by their interactions. Once the discharge groove was the same width, the injection flow rate first rose and then fell, as the diameter of the lower end of the suction piston increased. The injection flow rate also increased initially before decreasing, as the width of the discharge groove expanded, when the lower end of the diameter in the suction piston was less than 14 mm. However, the injection flow rate rose, as the width of the discharge groove increased, when the diameter of the lower end of the suction piston was between 14 and 17 mm. The injection flow rate first increased and subsequently declined with the increase in the diameter of the lower end of the suction piston and the depth of the discharge groove. The injection flow rate essentially remained the constant, as the width of discharge groove increased, when the depth of the discharge groove was less than 2.5 mm. Only a little impact was found in the width of the discharge groove on the injection flow at this time. The injection flow rate increased with the discharge groove width, when the depth of the groove was larger than 2.5 mm. An optimal combination was achieved: The diameter of the lower end of the suction piston was 16.6 mm, the width of the discharge groove was 5.5 mm, and the depth of the discharge groove was 3.7 mm. The optimum structure parameters were also obtained for the suction piston flow channel. The structural parameters of the suction piston were optimized for the proportional fertilization pump under various injection ratios and differential pressures. The injection flow rate was higher than that of the prototype proportional fertilization pump, which further decreased the discrepancy between the actual and theoretical injection flow rate. The injection precision increased by 3.33, 1.67, and 7.29 percentage points at the differential pressure of 0.05, 0.10, and 0.15 MPa, respectively. Anyway, the injection precision of proportional fertilization pump was improved significantly to extend the typical working differential pressure range, indicating the better hydraulic performance of the device.