Abstract: In order to explore the application of acidizing technology in coal seam permeability enhancement, the paper carried out the research on gas adsorption performance and micro-mechanism of acidizing modified coal samples. Ten groups of modified coal samples of lignite and coking coal were prepared by hydrochloric acid solution with different pH values. The industrial analysis, gas adsorption test and low temperature nitrogen adsorption test of modified coal and raw coal were carried out respectively. The results of gas adsorption test show that acid modification can change the adsorption properties of coal samples. When the pH value is equal to 3, the adsorption properties of modified coal samples decrease, while the adsorption properties of other modified coal samples are higher than that of raw coal. Analysis of low temperature nitrogen adsorption test results shows that lignite is dominated by pores of 10-100 nm, while coking coal is dominated by pores of 2-10 nm. The specific surface area of modified coal samples with pH value of 3 decreases and the pore volume of samples more than 100 nm increases. Fractal dimension of each group of coal samples is calculated by fractal theory, and the fractal dimension of coking coal is positively correlated with lignite pores and mesopores and gas adsorption constant a. The modification of coal with suitable acid can change the adsorption property of coal and increase the permeability of coal.