Abstract: The electron emission yield of protons with an energy range of 50~250 keV incident on tungsten surface of a target at different temperatures are measured on the 320 kV electron cyclotron resonance ion source(ECRIS) platform of the Institute of Modern Physics, Chinese Academy of Science(IMP, CAS) in Lanzhou. It is shown that the electron emission yield induced by protons with different energies decreases with the increase of target temperature. The results were qualitatively explained by the temperature dependence of the work function. At different target temperatures, the ratio of total electron emission yield to electronic stopping power decreases with the increase of incident ion energy. The ionization competition between electrons in different shells of the target atom is used to explain the experimental results.