The radiation influences on electrical parameters of 4H-SiC vertical double-implanted metal-oxide-semiconductor field effect transistor ( VDMOS) are studied. By simulations on SRIM software and SILVACO software, the electrical parameters shifts of the device with defects in different regions are observed. The results indicate that the defects in different regions induced by radiations lead to different degradations of the electrical parameters. Non-ionization bulk defects in the JFET region make the drain-source on-state resistance Rdson increase, and those near the impact ionization center make the breakdown voltage Vbreakdown increase. Moreover, the radiation-induced SiC/SiO2 interface defects, known as negative interface charges or positive interface charges, influence the electrical parameters significantly as well. The positive interface charges along the SiC/SiO2 interface above the channel region lead to a decrease in threshold voltage Vth , Rdson and Vbreakdown , while positive interface charges along the SiC/Metal interface above the main junction of the terminal only leads to the decrease in Vbreakdown . The negative interface charges along the SiC/SiO2 interface above the channel region can make Vth , Rdson and Vbreakdown increase.