Abstract: Pressure differential tank is the most popularly used injection device for fertigation of micro-irrigation system in China. However, there are few special guidelines for management of a micro-irrigation system using pressure differential tank as an injector. Dynamic variations of the fertilizer solution concentration of outlet of pressure differential tank were tested under different pressure differentials and fertilizers amounts. In the experiments, the fertilizers amounts of 13 and 26 kg were used, and the pressure differentials changed from 0.05 to 0.30 MPa with an incremental interval of 0.05 MPa. For all experiments, the pressure at the downstream of the tank was fixed at 0.10 MPa. Results show that the increase of flow with pressure differential through the tank can be represented by a power function. Fertilizer solution concentration released from the tank decreases continuously with time, especially at the beginning of injection initiation. It is important to maintain a constant pressure differential through the tank during the process of fertilizer injection for obtaining a uniform fertilizer distribution in a micro-irrigation system because the pressure differential is the primary factor affecting the decrease of fertilizer solution concentration with time. The regression equations to estimate the dynamic variation of fertilizer solution concentration and the time at which the concentration became zero were also established.