Abstract: In this study, nuclear grade graphite was irradiated by 1.08 MeV C4+ at room temperature and 180 ℃ to 0.02 dpa, 0.2 dpa and 2 dpa, respectively, using the 320 kV highly charged ion beam platform for multidiscipline researches of Institute of Modern Physics, Chinese Academy of Sciences. Scanning electron microscopy (SEM), focused ion beam microscopy (FIB) and transmission electron microscopy (TEM) were used to study the effects of ion irradiation temperature and irradiation dose on the microstructure and crystal structure of nuclear grade graphite. Results of the asreceived nuclear grade graphite show that the microstructure is composed of filler particles and binder, and there are a lot of microcracks in the area of filler particles. The binder region is composed of fine graphite microcrystals, microcracks, roseshaped QI particles, mixedlayer graphite and disordered structure. With the increase of the irradiation dose, the surface smoothness of the nuclear grade graphite becomes worse, and the pore density and average pore size increase, the matrix defects accumulate and the graphite crystal expands along the c axis and shrinks along the base plane parallel to the a axis. The low dose irradiation (0.02 dpa) has little effect on the microstructure and crystal structure of the nuclear grade graphite, and there is no significant difference between the irradiated area and the nonirradiated area. Medium dose irradiation (0.2 dpa) leads to the closure of microcracks in nuclear grade graphite matrix, and the irradiation boundary line appears along the irradiation depth direction. High dose irradiation (2 dpa) leads to the closure of almost all microcracks in the irradiation area, and the irradiation boundary line is more obvious, the irradiation depth is deepened. When irradiated at 180 ℃ to 2 dpa, the results of scanning electron microscopy show that the microstructure of graphite is fragmentary, and the results of transmission electron microscopy show that the structure of nuclear grade graphite becames disordered and amorphized, which shows that the microstructure of graphite is damaged by C ion bombardment.