One way of digital close-loop dynamic test for the area stability control system（ASCS） in Fujian Grid is proposed. The analog outputs of the grid load flow and the fault line are easily obtained from the real time digital simulation（RTDS）. A new photo-electricity interface between the ASCS and RTDS to realize the output of lines load flow is designed， and the line relay protection is merged into it to build the entire close-loop dynamic test system. By the close-loop dynamic test of the ASCS， the reliability of the ASCS is verified and the ASCS function for the Fujian Grid stability is ensured.