The invention discloses a monitoring device for an ageing working condition of a large-power single-tube microwave power supply. The monitoring device comprises: a box body (1), a programmable logic controller and a switching power supply which are mounted in the box body (1), and a touch type display screen (2) and a data interface (3) which are mounted on the surface of the box body (1); a threading hole (4) is formed in one side of the box body (1); the programmable logic controller is connected with the touch type display screen (2), the data interface (3) and a signal acquisition module group; the programmable logic controller, the touch type display screen (2) and the signal acquisition module group are all connected with the switching power supply. The monitoring device provided by the invention is reasonable in structural design, high in automatic and intelligent degree and high in working efficiency, and can be used for monitoring an operation state of large-power microwave power supply equipment in an ageing testing process in real time; data analysis and storage can be provided, alarming is carried out according to pre-set parameters and the practicability is high.