Abstract: The maintenance,operation and trouble-shooting of the vacuum system,installed in HITACHI scanning electron microscope,were addressed briefly in a thought provoking way.To begin with,the negative influence of the unstable vacuum on the image quality,service life of filament,cleanliness of electron optics and normal operation of SEM was discussed with specific examples.Second,the possible solutions to the common technical problems,including,but not limited to the no response of pneumatic valve,diffusion pump breakdown,abnormal oil temperature,starting failure of mechanical pump,and deterioration or contamination of cooling water,were suggested.And finally,when it comes to safe operation and regular maintenance of the vacuum system,some musts and must-nots were recommended.