The utility model relates to a teaching aid or a board game toy, in particular to a trapezoidal chess, which comprises chess pieces and a chess board. Each chess piece is an isosceles trapezoid with a one-unit long upper base, a two-unit long lower base and one-unit long lateral sides; the chess board is an isosceles trapezoid similar to the isosceles trapezoid of each chess piece; and the sizes of the upper base, the lower base and the lateral sides of the similar isosceles trapezoid are the same integral multiple of those of the upper base, the lower base and the lateral sides of the isosceles trapezoid of each chess piece. The trapezoidal chess is simple in structure and low in cost, and is a board game toy similar to the game of go. A player needs a certain topological and geometric knowledge, and memory ability and visual thinking are trained by using hands and brain.