The invention relates to a vacuum furnace and a window cleaning device thereof. A mounting base used for installing a window is arranged on the outer side of the vacuum furnace, and the cleaning device includes a drawable rod and a cleaning head. The drawable rod penetrates into the mounting base and can be moved toward or outward the mounting base; the cleaning head is positioned at the inner endof the drawable rod. During pulling of the drawable rod, the inner side face of the window is cleaned. The cleaning device can achieve online cleaning of the window under the working condition of normal temperature or high temperature; after the inner side of the window is contaminated and observation is interrupted, on-line cleaning is conducted on the inner side face of the window in real timeto ensure the measurement precision of an in-situ measurement device under a high-temperature high-vacuum environment. The operation during cleaning is convenient, and the vacuum degree of the interior of a furnace chamber is also guaranteed.