Understanding the biotransformation mechanism of chlorinated hydrocarbons in contaminated site is of great significance to the in-situ bioremediation. Therefore, we summed up the overlapping composition of chlorinated hydrocarbons and analyzed statistically the concentration variations and degradation rate of chlorinated hydrocarbons in various landfill which were regarded as one of the most typical compound pollution sites. The statistical data indicated that chloralkane and chloroalkene concentration ranged 0.20 to 32.45 and 0.50 to 32.45 μg/m³, respectively, which were the main components. We also found that biodegradation rates of chlorinated hydrocarbons decreased with the number of attached chlorine atoms in landfill cover. Then, we summarized the biodegradation mechanism of chlorinated hydrocarbons under different environmental conditions. The results implied that chlorinated hydrocarbons biodegradation incorporated aerobic co-metabolism, halorespiration and anaerobic reductive dechlorination involved in a wide range of substrates and a variety of functional microbes. Based on of these analyses, we constructed biodegradation models of chlorinated hydrocarbons in landfill cover. Finally, the possible development of chlorinated hydrocarbons biological removal in the future was predicated.