Abstract: Using 20 L nearly spherical explosion characteristic test system, the paper studies the change laws of lower explosive limit of three different kinds of coal dust with low concentration gas. The study shows that coal dust lower explosive limit decreases with the increase of gas concentration under this experimental condition. When the gas concentration is in the scope of 0 to 1.0%, coal composition has a greater influence on lower explosive limit, the corresponding explosive composite system of gas and coal dust is characterized as "strong coal dust"; when the gas concentration is greater than 1%, the numerical difference of coal dust lower explosive limit concentration is small, and the influence of coal composition on coal dust lower explosive limit is no longer obvious; the corresponding composite explosive system of gas and coal dust coexisting is characterized by "strong gas".