The invention provides a 2D route planning method for a UUV to round rectangular obstacles geometrically. The method comprises the following steps: S1, reading a route start point Ob, a route end point Oe and the parameters of rectangular obstacles from a mission text; S2, expanding the rectangular obstacles, and calculating the parameters of the rectangular obstacles after expansion; S3, building a rounding point set S, letting a planned current point Oc be the start point Ob, and putting the planned current point Oc in the rounding point set S; S4, if the planned current point Oc is the route end point Oe or the planned current point Oc and the route end point Oe are visible, going to S6, or, executing S5; S5, geometrically rounding the rectangular obstacle nearest to the planned current point Oc to get rounding points, putting the rounding points in the rounding point set S, updating the planned current point Oc, and going to S4; and S6, putting the route end point Oe in the rounding point set S, and ending planning. According to the invention, rectangular obstacles are rounded based on a simple geometric principle, and a UUV can get a safe and collision-free 2D route quickly and efficiently in a complex environment with multiple rectangular obstacles.