In this paper, one thin microwave absorbing sheet employing carbonyl-iron powder (CIP) and chlorinated polyethylene (CPE) was prepared. The pattern and static magnetic properties of CIP were characterized by scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The electromagnetic parameters and loss mechanisms of CIP were measured and discussed. The microwave absorption properties of composite sheets with different thicknesses and CIP ratios in matrix were investigated by measuring reflection loss (RL) in 2-18GHz. The results showed that the microwave absorption properties could be optimized by controlling CIP content and thickness of sheet. For the sample with the weight ratio (CIP:CPE) of 10:1 and 1mm thickness, the absorption bandwidth (RL below -4dB) achieved 14GHz (4-18GHz).