In view of the deficiency of traditional method of controlling the consistency of maize seeding depth, the method for controlling the consistency of seeding depth based on the force feedback was carried out and the downforce control system for maize seeding unit was developed. The system consisted of hydraulic cylinder mounted on the parallel four bar linkage profiling mechanism in a seeding unit, hydraulic system, downforce sensor, controller and vehicle computer. According to the force sensor information and the downforce threshold, the controller calculated and output the control value to hydraulic valves. The hydraulic cylinder was drived by valves to adjust parallel four connecting rod profiling mechanism to make the depth wheels and the surface pressure within the set threshold interval, so as to ensure the consistency of seeding depth. The field tests showed that the average quality rate of seeding depth of mechanical control of downforce and electric control downforce were 77.04% and 90.37%, respectively, while the seeding depth criterion was （5.0±1.0）cm, and the average quality rate of sowing depth of electric control downforce was 13.33 percentage points higher than that of mechanical control. Nevertheless, when the seeding depth criterion was （5.0±0.5）cm, the corresponding seeding depth quality rate were 31.11% and 56.30%, respectively, and the average quality rate of sowing depth of electric control downforce was 25.19 percentage points higher than that of mechanical control. The test results showed that the downforce control system can greatly maintain seeding depth stability and improve seed depth uniformity.