Observation window structure of vacuum evaporator

The utility model provides an observation window structure of a vacuum evaporator, the observation window structure is arranged on a cavity door of the vacuum evaporator, the observation window structure comprises outer-layer glass, a mounting rack and an extension piece from outside to inside, the outer-layer glass and the mounting rack are fixed on the cavity door, the extension piece is connected with the mounting rack and is located in a main cavity of the vacuum evaporator, and the outer-layer glass is fixed on the outer-layer glass. An inclination angle a is formed between the extension piece and a vertical line of the inner wall of the cavity door, the inclination angle a is 0-180 degrees, and the mounting frame is provided with a first through hole; the number of the extension pieces is two, the two extension pieces are arranged on the mounting frame up and down, the inclination angles a of the two extension pieces are the same or different, and one or two of the extension pieces have a reflection fun