The invention discloses an external power measuring apparatus of an engine. The external power measuring apparatus of an engine includes the steps: a mounting support and a torque measuring system, wherein the mounting support is used for mounting and fixing the engine and enabling the air intake duct and the output shaft of the fixed engine to be on the same horizontal line; the torque measuring system is arranged under the mounting support and is used for measuring the output torque of the engine; the torque measuring system includes a torque measuring member; the torque measuring member measures the magnitude of the output torque of the engine according to the rotation moment generated during the working process of the engine, and is connected with a moment transmission support which is used for transmitting the rotation moment on the mounting support to the torque measuring member; and the moment transmission support is connected with the bottom end of the mounting support. In the external power measuring apparatus of an engine, the torque measuring system does not influence air inlet of the engine, thus having no demand for designing an air intake duct which inclines upward and has a longer length and then having no demand for adding a support frame for supporting the air intake duct at the front end of the air intake duct, so that the technical problem that the mounting and fixing difficulty of the support frame does not exist. Moreover, the external power measuring apparatus of an engine is simple in structure.