Metal elements in biomass ash have been considered to affect the decomposition of large molecule during the pyrolysis of biomass. In this paper, effect of metal elements on the evolution of carbon monoxide (CO) and methane (CH 4) was investigated during the pyrolysis of sawdust in a fixed bed reactor and species were detected by Fourier Transform Infrared analyzer. Results showed that all the metal additions restrained the yields of CO and CH 4 and the quantity order of production was Fe 2 O 3 <ZnO<NaCl<CaO<KCl< Al 2 O 3 <No-addition. The addition of Al 2 O 3 , Fe 2 O 3 and ZnO shortened the completion time of CO and CH 4 . Statistical analysis demonstrated that all the metal additions lowered the reaction rate of biomass pyrolysis dynamically.