Objective:To measure the beam stability of the electron FLASH radiotherapy accelerator developed by the Institute of Applied Electronics of Chinese Academy of Engineering Physics and to evaluate the performance of scintillator, fast current sensor (FCT) and graphite under the electron FLASH beam.Methods:Each continuous beam exit deviation and each pulse deviation at the electron FLASH radiotherapy accelerator in the same working state were measured. The correlation among three monitors and the measured dose of the accelerator at different electron beam energy (controlled by changing the charging voltage) and different beam pulse numbers were compared, which were validated by a Monte Carlo simulation procedure.Results:At the first high pressure, the first 10 scintillators and FCT signals were relatively large, approximately 2% deviation compared with the average value of 400 pulses. Among 40 beam outflows, the deviation between each pulse was within ±5%. In the accelerator steady state, each beam outflow deviation was within ±1%. Both simulated and measured values showed that the monitor could not be used for dose monitoring at different electron beam energy. However, when the energy was the same, only the number of beam pulses was changed, and linear relationship was observed between the number of the three monitors and the dose measured by the film (all R 2 > 0.999). Conclusions:The beam deviation of each beam outflow of this electron FLASH accelerator is within ±1%. Under the stability of the accelerator beam, the scintillator, FCT and graphite can meet the dose monitoring of the target area, which can provide reference for dose monitoring for subsequent biological experiments.