Abstract: It figures out how to design the fertigation device used in moden water saving irrigation, which can inject liquid fertilizer and acid liquid or alkali liquid into irrigation pipe net by rust-resistant pump, and should bring irrigation liquid in finite concentration and acidity or basicity (EC & pH) and fertilize the field in precision. The Variable voltage variable frequency(VVVF) system regulates the parameters (EC & pH) of irrigation liquid dynamically, when it receives the signal from EC & pH sensors that detect the values of EC & pH of the irrigation liquid. This device works very well when it is put in operation and reaches the standard of designing. Especially the VVVF technology for jet pump that not only regulates the concentration (EC value) of irrigation liquid dynamically, but also depresses the cost of device obviously. As a result, it shows that the VVVF technology for jet pump can be effectively used to develop the fertigation device.