Abstract: A triangular ruler includes a triangular ruler body; a right-angle edge of the triangle ruler body is provided with an extended ruler, and the outer side of the extended ruler is provided with the angle scale line, the interior of the triangle ruler body and the extended ruler are both provided with matching rotating holes, and the adjustment part is provided at the connection between the triangle ruler body and the extended ruler. When measuring long distances, by rotating the extended ruler until coincides with the right-angle edge of triangle ruler body, the extended ruler and the triangle ruler body are combined for long-distance measurement.