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To suppress the increasingly terrible electromagnetic pollution, microwave absorption coatings based on polyvinyl chloride (PVC) sheet have been fabricated, employing polyurethane varnish (PU) as matrix and carbonyl–iron particle (CIP) as absorbent. The morphology, static magnetic and microwave absorption properties of CIP were characterized by scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and vector network analyzer (VNA), respectively. Bruggeman's equation was introduced to calculate the electromagnetic parameters of materials in the frequency range of 2–18 GHz and the loss mechanisms were discussed. Furthermore, the microwave absorption properties of composite coatings with different component content and thickness were investigated. The results show that the electromagnetic properties of the composite heavily depended on the particle loadings. The minimum reflection peaks of the coatings shift towards the lower frequency region with the increase of CIP content or coating thickness. PVC-based coatings with a component content of 1:7 (PU:CIP mass ratio) in CIP/PU layer, exhibit a minimum reflection loss value of −29 dB at 4 GHz and a permissible reflection loss (RL ≤ −10 dB) frequency band of 2–6 GHz, which is much better than the performance of the common metal-based coatings in the lower frequency.