Medical electron linear accelerator is an important device in radiotherapy. It has been widely used in radiotherapy of malignant tumors. Its stable operation is directly related to the effect and safety of radiotherapy. In clinical practice， the probability of medical electron linear accelerator failure is high， which has a certain impact on daily use. Therefore， based on the working principle of medical electron linear accelerator， the paper analyzes the common faults and summarizes the maintenance countermeasures.