Abstract: In order to study the pore characteristics of medium and low rank coal and its influence on gas emission characteristics, 14 samples of 4 coal types in medium and low coal rank were collected. Through the coal industry analysis, coal and rock analysis, liquid nitrogen adsorption and gas emission initial velocity test, combined with fractal theory, the specific surface area, pore volume and pore distribution characteristics and gas dissipation characteristics of medium and low rank coal were studied. The results show that the pore distribution of pore specific surface area of medium and low rank coal is mainly small and micro-pore, and the pore morphology is mainly open at one end, with a small number of open at both ends, and some samples contain a small number of ink bottle-shaped pores. The coal pores of medium and low rank coal have good fractal characteristics, and the pore specific surface area, pore volume and fractal dimension have obvious logarithmic relationship. The initial velocity of gas release in medium and low rank coal is small, and the initial velocity of gas dissipation decreases with the increase of fractal dimension, and increases with the increase of average pore size. With the increase of pore volume and specific surface area of each pore size, the initial velocity of gas dissipation decreases in a negative logarithm. The slight change of the ratio of each pore size and the shape of coal pore morphology has little effect on the initial velocity of gas dissipation.