The influence of potential and humidity on the electrochemical carbon corrosion in high temperature polymer electrolyte membrane fuel cells(HT-PEMFCs) is investigated by measuring $CO_2$ emission at different potentials for 30 min using on-line mass spectrometry. These results are compared with low tempterature polymer electrolyte membrane fuel cells(LT-PEMFCs) operated at lower temperature and higher humidity condition. Although the HT-PEMFC is operated at non humidified condition, the emitted $CO_2$ in the condition of HT-PEMFC is more than LT-PEMFC at the same potential in carbon corrosion test. Thus, carbon corrosion shows a stronger positive correlation with the cell temperature. In addition, the presence of a little amount of water activate electrochemical carbon corrosion considerably in HT-PEMFC. With increased carbon corrosion, changes in fuel cell electrochemical characteristics become more noticeable and thereby indicate that such corrosion considerably affects fuel cell durability.