In this article, the circulation of the South China Sea (SCS), which is idealized as the rectangular basin with constant depth, is studied under Kuroshio boundary forces. Starting from the linearly quasi-geostrophic vorticity equation, the solution of the SCS circulation is given in the form of corrected Fourier series under proper boundary conditions. The results show that the intruded current flows westward and separates into the northward branch and the southward branch before arriving at the west boundary. The southward branch flows out of the SCS through the southwest passage, at the same time, the induced cyclonic (anti-clockwise) ring almost occupies the middle and south parts, and concomitant anti-cyclonic (clockwise) vortex appears between the cyclone and the west boundary. While the northward branch outflows through the northeast passage, the anti-cyclonic (clockwise) ring is triggered at the north part of the SCS. The above two vortexes are both intensified if the south-entering and the north-leaving current loop intrusion are superposed. The outer flow of the north vortex flows westward, then northward, and then eastward, and it is very similar to the configuration of the SCS Warm Current (SCSWC) at the north part of the SCS, thus, a kind of generating mechanism of the SCSWC is presented.