The invention provides a controllable force source generating device for a thrust vector testing system, and belongs to the technical field of sensing and measurement and control. The device overcomesthe difficulties that the ground ignition test is high in cost, is liable to cause environment pollution and is complex in technology and process. The device serves as an external force source generating device, and an external loading force generated by the device serves as the simulation force of a rocket engine, and acts on a thrust vector testing system with the rocket engine. The device enables generated orthogonal controllable unidirectional forces to compose a controllable composite force, and a hydraulic loading device is enabled to move up and down to change a force acting point, thereby achieving the control of the size, direction and acting point of a force vector. The device serves as an external force source, and generated three-direction orthogonal forces can be used for simulating the stress condition of a measured object. The generated torque can be used for simulating the yaw, pitching and rolling of the measured object. In addition, the device can verify the stationary performances of any thrust testing system, and enables the thrust testing system to achieve the integration of measurement, control, and calibration.