In recent years, there are many power quality problems in the distribution system, and active power filter(APF) becomes one of the main technique. This paper first establishes the Euler-Lagrange(EL) model of the neutral APF based on single-phase VSI, which the passivity design is based on. Then the control scheme tracking the desired current is derived accordingly and a PCB board is designed to carry out the algorithms based on FPGA. The simulation and experiment result shows the validity of the design in the end.