The invention provides a visual glass observation window for a flow field of an aircraft irregular-shaped cured surface internal flow passage and a design method. The visual glass observation window for the flow field of the aircraft irregular-shaped cured surface internal flow passage and the design method are used for observing the flow field, composed of a series of discrete points, of the irregular three-dimensional irregular-shaped curved surface internal flow passage. The glass observation window comprises two light-transmitting surfaces, the inner surface C1 is completely consistent with the wall surface of the internal flow passage, and the outer surface C2 is a correction curved surface used for eliminating light deflection generated by the inner surface, so that parallel light is still parallel light after passing through the optical glass observation window. When the observation window is used for observing the flow field of the irregular-shaped cured surface internal flow passage, neither deflection nor crossing of light is caused, the observed flow structure is free of a distorting phenomenon, and optical non-contact measurement visual test research can be carried out on the three-dimensional flow field of any irregular-shaped cured surface internal flow passage. The design method not only can be used for flow display of the internal flow, but also can be used for design of an infrared guide head and an irregular-shaped surface radar wave-transparent window.