The technology of brain-computer interface （BCI） based on motor imagery （MI） has developed rapidly in the past few decades and been widely used in various fields. To compare the brain electrical activity difference between motor execution （ME） and MI， a method based on the time-frequency domain analysis of electroencephalogram （EEG） is proposed. The visually induced upper limb ME and MI control experiments are conducted and the EEG signals of ten healthy subjects are collected and preprocessed. Then the signals are decomposed and converted into eigenvalues of each band through the time-frequency analysis method. Finally， the power values of each band of ME and MI are analyzed and the power differences between each band of ME and MI are computed. The results show that the alpha wave is dominant wave in the process of MI while the delta wave is dominant wave in the process of ME. Compared with MI， the alpha wave during ME shows a downward trend and the delta wave shows an upward trend. The results of this study show that there is significant difference in EEG between ME and MI， which is important for improving the real-time and universal performance of MI based BCI systems.