In order to improve the fertilization quality of deep fertilization for paddy field, an adjustable blades side deep fertilizing device for paddy field was designed. Structure parameters of fertilizer rate adjusting mechanism were optimized by using optimization software V1.0, which was developed for fertilizer rate adjusting mechanism of side deep fertilizing device for paddy field. The stress analysis was carried out for fertilizer rate adjusting mechanism, through which the output torque of stepper motor was determined greater than 680N·mm. Simulation model was established for adjustable blades side deep fertilizing device, and virtual experiment of distributing fertilizer was carried out by using discrete element EDEM software to analyze the acting force of fertilizer particle on spiral steel wire and hairbrush, therefore, the output torque of the direct current motor of fertilizer cases and anti-blocking device was determined greater than 5345N·mm and 8N·mm, respectively. Fertilization performance of groove wheel type and adjustable blade type side deep fertilizing device for paddy field were studied on JPS-12 type discharging seed performance detection test bench, through which the influence laws of the rotation speed and forward velocity of the groove wheel type side deep fertilizing device on fertilizer stability and uniformity were obtained, the influence laws of the opening diameter and the forward speed of adjustable blade type side deep fertilizing device for paddy field on fertilizer stability and uniformity were obtained. The test results showed that fertilizer stability and uniformity indexes of adjustable blade type side deep fertilizer device for paddy field can meet national standard requirements, the quality of fertilization was superior to that of groove wheel type side deep fertilizing device, and the fertilization ability can meet agronomic requirements.