In order to study the blockage law of Y mesh filter used to filter organic fertilizer in water and fertilizer integrated equipment, the clogging test of Y type mesh filter was carried out at the initial flow rate of 500L/h and the water source pressure of 117.6kPa, and the concentration levels of four kinds of potassium fulvic acid organic fertilizer solution, 25g/L, 30g/L, 40g/L and 50g/L were set up. The relationship between the local head loss coefficient of Y type mesh filter and the effective cross section area of single filter, the proportion of single filter effective cross section area and total area S/S0 was analyzed, and the composition of blockage material in the filter was analyzed by XRD. The results showed that the concentration of fertilizer solution had a significant effect on the screen cleanness of the filter. It was suggested that when the concentration of fertilizer solution was not more than 40g/L;the flow rate of 4m head loss in the filter was decreased by 17%~20%. The local head loss of filter was increased gradually when the screen cleanness was reduced to 10%. Correlation analyses displayed the local head loss coefficient of filter was only related to S/S0 and independent of fertilizer concentration. Furthermore, the formula for calculating the local head loss coefficient of filter under potassium fulvic acid organic fertilizer was put forward by using multinomial fitting;filter-element blocking substances mainly included calcium sulfate and calcium oxalate. The research results can provide some theoretical reference for the selection of filter in water and fertilizer integrated machine.