In view of the fact that there are few application conditions of domestic ball valve,a rectangular-opening ball valve was proposed.A finite element simulation analysis was conducted on the rectangular-opening ball valve with a diameter of DN50 and an opening width of 25 mm.The pressure distribution,velocity contours and streamline pattern of its were achieved and the flow field control performance was analyzed.In addition,flow area change rules and flow capacity control performance of rectangular-opening ball valves with different opening widths were analyzed.The analysis results show that a two-stage pressure drop is achieved by the S-shaped flow channel formed during the turn-on process,which can enlarge the scope of pressure control; in terms of the flow capacity control,its performance owns both relevance and difference with the change rules of the flow area; the control characteristics of most rectangular-opening ball valves are equal percentage characteristics and the change rate increases with the increases of the opening widths; but there are a few of linear characteristics during small-width openings of the rectangular-opening ball valves.