Abstract: Hazardous materials will cause poisoning, fires, explosions and other disasters after leakage and diffusion during storage and transportation, of which physicochemical properties and special diffusion laws are the main factors which determine the scope of accident and disaster. Accurate understanding of leakage and diffusion laws of hazardous materials is the basis for the development of emergency rescue plans and safety control measures. Laboratory simulation experiment is made for leakage and diffusion processes of heavy hazardous materials of oil tankfarm in different leakage locations and leak directions, of which research results indicate that when the tank in the center of a tank group suffers from leakage, the gas is easily accumulated in the tankfarm and the diffusion rate is lower; when the tank at the edge of a tank group suffers from leakage, the gas diffusion rate is higher with a larger influence area; when the leakage direction is vertically upward or vertically downward, the gas accumulates easily in the tankfarm around the leakage opening, of which gas volume fractions can quickly reach the explosive limit, causing great risk. The research results can provide a reference to the development of emergency rescue plans for hazardous materials in tankfarm.