In this paper, the damage caused by C ion irradiation on AlGaAs/InGaAs HEMT was investigated. The projection ranges of C ions with varying energies in AlGaAs and InGaAs materials were calculated using Monte Carlo simulation. Additionally, simulations were conducted to study the radiation-induced damage caused by 50 keV, 70 keV, and 100 keV C ions incident on the basic structure of the AlGaAs/InGaAs heterojunction.The results showed that when using 70 keV energy for C ions, a higher number of vacancy defects were generated. Based on these findings, the influence of defects introduced by different irradiation doses of 70 keV C ions on the DC and RF characteristics of the device was analyzed.