The single crystal 6H-SiC was irradiated by 400 keV He₊ ions with 1×10₁₆ He₊/cm₂ fluence at 400°C and then annealed for 30min at 1200 and 1500°C. The microstructure was observed by using transmission electron microscopy and scanning electron microscopy. Only the damaged layer was observed and no visible helium bubbles were formed in SiC matrix after helium ion irradiation at 400 °C. However, after annealled at 1200 °C for 30 minutes, platelet-like planar bubbles were formed in the irradiated region, which were distributed mainly on the (0001) plane and less on the (1 1 -2 0) crystal plane. There were no visible size defects formed on 6H-SiC surface after helium ion irradiation. But, blisters and craters were formed after annealing at 1200 °C for 30 min and became easier with annealing temperature increase. Some cracks were generated after annealing at 1500 °C. The mechanism of microstructural evolution was also analyzed and discussed.