The invention discloses a device and a method used for observing an air flow field structure in environment of different degrees of vacuum. The device is composed of a light source, a collimating lens, a pressure transmitter, a gas nozzle, a vacuum chamber, a focusing lens, a cut, a camera, a high reflectivity and high transmittance lens, a first CCD camera, a second CCD camera, a totally reflecting mirror, a focusing convex cylindrical lens, a collimating convex cylindrical lens, a plano-concave lens, a laser, a vacuum pump, a gas nozzle and a vacuum pump. According to the invention, a schlieren method and acetone PLIF are used to simultaneously observe the air flow field structure in environment of different degrees of vacuum; through the contrast correction of information acquired in two observing manners at the same time, a real air flow field structure is acquired; the success probability and the reliability of high altitude and space laser ignition are improved; the device and the method focus on observing the air flow field structure under different degrees of vacuum; and the air flow field structure information acquired through the device and the method can effectively help to choose the best ignition location for the laser ignition scheme of an engine in different environments.