The invention discloses a preparation method of emission-free expansible graphite and a smokeless preparation method of sulfur-free expanded graphite, relates to expansible graphite and a preparationmethod of expanded graphite, and aims to solve technical problems that a large amount of wastewater is discharged in an expansible graphite preparation process and large smoke is generated and the environment is polluted when the expansible graphite is puffed. The preparation method of the expansible graphite comprises the following step: uniformly mixing and stirring crystalline flake graphite with a perchloric acid solution, so as to obtain the emission-free expansible graphite. The preparation method of the expanded graphite comprises the following steps: assembling a puffing device consisting of a puffing furnace, a gas guide tube, an absorption tank, an exhaust tube and a fan; uniformly mixing the emission-free expansible graphite with an acetic acid solution or a propionic acid, andperforming puffing in a puffing furnace, so as to obtain the sulfur-free expanded graphite. The expanded graphite is free of sulfur or nitrogen and is free of heavy metal impurities such as manganeseor chromium, and the product is pure. In the puffing process, not thick smoke is generated, a working environment is clean, and no pollution is caused. The expanded graphite can be applied to fields such as petroleum, chemical engineering, aviation, mechanical engineering and the nuclear industry.