Biomass tar catalytic decomposition upon pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was studied by taking naphthalene and phenol as model compound. The effect of reaction temperature, charring conditions, such as the pyrolysis temperature, the heating rate and the precursors on model compound conversion was determined. The results showed that tar conversion increased with the increasing reaction temperature; higher charring temperature and higher heating rate could enlarge the surface area and pore volume of biomass chars and also enhance tar conversion. Conversion of naphthalene and phenol were 55.6% and 76% respectively on biomass char prepared at 850℃ with quick heating rate. Scanning electron microscope (SEM) and test results of char mineral oxides contents showed that catalytic activity of biomass chars was related to their surface morphology and the mineral oxides contents