The embodiment of the invention provides a plasma thruster steady-state ion flow field measurement device and a measurement method and belongs to the technical field of steady-state ion flow field measurement. The device comprises a measurement module, a power supply module and a probe assembly, the probe assembly comprises a probe, a probe support and an electric rotary table, the probe comprisesan insulation shell, an ion receiving pole, an incident gate and an emergent gate, one end of the insulation shell is open, the incident gate is located at the opening of the insulation shell, the emergent gate is located at the middle part of the inner cavity of the insulation shell, the ion receiving pole is located at one section, far away from the incident gate, in the inner cavity of the insulation shell, an incident hole of the incident gate and an emergent hole of the emergent gate are coaxial, the ion receiving pole, the incident gate and the emergent gate are mutually insulated, theinsulation shell is fixed on the probe support, and the electric rotary table is used for driving the probe support to rotate around the incident hole of the incident gate. The device provided by theembodiment of the invention can obtain an ion current density distribution function on each azimuth angle of a measurement point by enabling the probe to rotate around the measurement point, and a vector angle of an ion velocity is obtained at the same time.