Tar contained in gasification syngas is one of the most problematic species that restricts the gasification efficiency and system availability. The catalytic decomposition of tar is a novel technology to clean the produced syngas. In this article, the interactions of cellulose and polyvinyl chloride (PVC) on the catalytic cracking of tar contained in municipal solid waste gasification syngas were experimentally studied. Results show that at the pyrolysis temperatures of 500 and 600 degrees C the catalytic cracking efficiency was 91-98% for tar derived from a single feedstock. When cellulose was mixed with PVC, the tar cracking efficiency decreased to 68-90% because of the interactions during the copyrolysis and decomposition reactions. Gas chromatography (GC) and gas chromatography mass spectrometry (GC-MS) were employed to identify the main compositions of gaseous product and hydrocarbon species after cracking. The GC-MS results show that 99% of tar species have a carbon number less than 10 when the calcined dolomite catalyst was used. During the copyrolysis, PVC plays a dominant role in the formation of tar. The GC analysis shows that copyrolysis yields more CH4, C2H4, C2H6, and C2H2 and less CO than those from a single feedstock. Brunauer-Emmett-Teller, scanning electron microscopy, energy dispersive spectroscopy, and X-ray fluorescence analyses were used to characterize the catalyst before and after reaction. Results indicate that after mixing, the poisoning of catalyst by chlorine increased by 3-15 times, accounting for the low conversion ratio of tar derived from a mixture of cellulose and PVC.