Abstract: In order to improve the quality of tar products from low-rank coal,the effects of K,Ca and Fe on the formation characteristics of tar from coal catalytic pyrolysis were investigated in a microwave tube prolysis furnace.The distribution of group components and the changing law of composition of aromatic hydrocarbons in different tar products were studied. The results showed that the coal samples loaded with K,Ca and Fe quickly responded to the polarization loss and conductance loss of the microwave,so that the active component was selectively heated to induce the catalytic cracking reaction of the tar.Microwave-assisted metal components could catalyze the distribution of tar component groups.K and Fe increased the content of benzene and its derivatives by 12.8% and 25.15% respectively,and Ca significantly increased the aliphatic hydrocarbon content by 212%.K, Ca and Fe significantly promoted the ring-opening cracking reaction of tricyclic and tetracyclic aromatic hydrocarbons and made the aromatics above four rings almost disappear. Among them, Fe reduced the content of tricyclic aromatic hydrocarbons fluorene, osmium, phenanthrene and their derivatives by 62.68%, 67.25% and 58.33%, indicating that the microwave-assisted metal components could change the cracking pathway of heavy aromatics and improve the quality of tar products.