In the fields of tracking target and navigation based on vision, to measure the 3D pose of rigid objects besides the special location, the research of measuring the 3D pose of the object based on mono-view was performed. An algorithm of measuring 3D pose was proposed from the weak perspective model and the information of right-angled triangle formed by characteristic points of object that was the ratio of side-length. The algorithm was applicable under the condition that the interior parameters were unknown and it avoided iteration. The result of mathematical simulating experiment shows that the error of the 3D pose angles are less than 1.5° when the distance from object to camera is in the range of 1~3 km.The result of actual images shows that the remnants difference between the raw results and smooth results of pitch and yaw are less than 1°, and of roll angle is less than 2°. The experiment proves the correctness and stability of the proposed algorithm, which shows that the 3D pose of object can be measured effectively in the proposed algorithm, which can be perfectly applied to the objects with long distance and small visual angle.