The invention provides a plasma thruster transient ion flow field measuring device and measuring method and belongs to the technical field of transient flow field measurement. The device comprises a probe assembly, a measuring module and a power supply module. The probe assembly comprises an incident grid, an insulating shell, a fixed base and N probes, N is an odd number greater than or equal to3. The insulating shell is provided with an opening, the incident grid is fixed at an opening position of the insulating shell such that a closed cavity is formed by the insulating shell, N mounting holes are formed in the fixed seat at intervals, the probes and the mounting holes are mounted and fixed in a one-to-one correspondence manner, receiving surfaces of the N probes are positioned in thesame arc surface, the fixed base is arranged in the closed cavity, an incident hole of the incident grid is located in a circle center of the arc surface, the power supply module is used for providingnegative bias voltage for the incident grid and further used for providing scanning voltage for the probes, and the measuring module comprises N measuring units which are in one-to-one correspondencewith the probes and used for measuring ion current signals of the corresponding probes. The device can measure an ion velocity vector angle.