With melamine as raw material and Li2CO3 as dopant, g-C3N4 powder was synthesized by pyrolysis at 450, 550, 600, 650, 680℃ for 60 min, and Li+/g-C3N4 powders were also synthesized with Li+ mass fractions of 0.5%, 1.0%, 1.5% and 2.5% by pyrolysis at 650℃ for 60 min, respectively. The effects of pyrolysis temperature and Li+ mass fraction on the phase composition, micromorphology and photocatalytic performance of the powders were investigated. The results show that with the rise of pyrolysis temperature, the purity of g-C3N4 powders increased, the crystal structure gradually improved, and the degradation efficiency of methylene blue increased. When the pyrolysis temperature was 650℃, the g-C3N4 powder had a perfect crystal structure with the average particle size of 200 nm, whose photocatalytic performance was the best. The structure of g-C3N4 was not changed by Li+ doping, while the particle size was refined and the photocatalytic performance was improved. With Li+ mass fraction of 1.5%, the average particle size of Li+/g-C3N4 powder was 150 nm; the degradation efficiency of methylene blue reached 91% after irradiation for 240 min, which was 57.2% higher than that of the g-C3N4 powder.