In this paper, experimental and numerical studies on the decomposition pyrene, a main component of tar, under the steam reforming condition were conducted. The effects of operational conditions of reaction temperature T-R and steam to carbon molar ratio (S/C) on the yield of main light gases and soot are assessed. The associated global reaction rate and main reaction pathways were analyzed. The results revealed that pyrene was mostly converted into soot instead of light gases in the steam reforming. The yields of CO2 and H-2 significantly increased with T-R, whereas those of CO and CH4 remained relatively stable. The water shift reaction of exhaust gases at low temperature zone should be taken into account to accurately predicted the yield of light gases. The conversion of pyrene rapidly happened when S/C was < 2 and became gradually after. The global reaction rate of pyrene decomposition was obtained. Sensitivity analysis showed that the secondary cracking of soot with steam occurred at elevated temperatures. The reaction pathway of pyrene steam reforming could be divided into two stages with different products during the steam reforming process.