Observation window and single crystal furnace

The invention provides an observation window and a single crystal furnace, the observation window comprises a protection window assembly, the protection window assembly comprises at least two layers of transparent lenses and a fixing unit for fixing the at least two layers of transparent lenses on a mounting seat; the at least two layers of transparent lenses comprise an inner side lens and an outer side lens which are sequentially overlapped from the inner side of the furnace body to the outer side of the furnace body, and at least one of the inner side surface and the outer side surface of the inner side lens is in a cambered surface shape. According to the observation window and the single crystal furnace provided by the embodiment of the invention, the observation window comprises at least two layers of transparent lenses, and the inner side lens is provided with the cambered surface, so that the stress area of the inner side lens can be increased, the pressure can be more uniformly dispersed to the fixin