The invention discloses a vacuum plume aerodynamic force measuring system and method. The vacuum plume aerodynamic force measuring system comprises a vacuum chamber, an engine, a force measuring model, a plume protection cover, a displacement mechanism, a mounting base and a six-component balance force measuring system. According to the vacuum plume aerodynamic force measuring system and method, a small-range six-component balance is used as a force measuring element for directly measuring vacuum plume aerodynamic force, so that a measurement result is more accurate; according to the characteristics of high speed and high temperature of engine vacuum plumes, duralumin is used as a material for designing the force measuring model and the plume protection cover, so that the force measuring model and the six-component balance are prevented from being damaged; the displacement mechanism is used for driving the six-component balance and the force measuring model to scan a plume field, and aerodynamic force measurement can be conducted at multiple positions under multiple working conditions in one close-cabin experiment. The vacuum plume aerodynamic force measuring method comprises the following steps that the six-component balance is calibrated, a six-component balance working formula is calculated, experimental equipment is installed, the experiment is conducted, and data are processed.