Flap valve box observing window of single crystal furnace

The invention discloses a flap valve box observing window of a single crystal furnace. The flap valve box observing window of the single crystal furnace comprises observing glass arranged on a flap valve box; the observing glass is positioned on the inner surface of the flap valve box and plated with a reflecting layer; the reflecting later has an annular structure; and a transparent elliptical small observing window is arranged in the middle of the observing window. The observing glass of the flap valve box observing window of the single crystal furnace is positioned on the inner surface of the flap valve box and plated with the annular reflecting layer, and the transparent small observing window is arranged in the middle of the observing glass, thus the flap valve box observing window achieves an observing effect and reflects the radiant heat in the furnace simultaneously by utilizing the reflecting layer, and avoids loss of the sealing function of the rubber sealing ring contacted with the observing glass,