This well-known that too much tar formed is one of the most urgent problems for the biomass gasification process. In our previous work; it was found the pressurized torrefaction can effectively improve the fuel property of the biomass. In this paper, the effect of torrefaction pretreatments under atmospheric pressure (AP), gas pressure (GP), and mechanical pressure (MP) at 200-300 degrees C On biomass gasification was studied. It was found that the O/C value and higher heating value of the GP semi-char were as low as 0.27 and as high as 26.2 MJ/kg, respectively. The fixed carbon content of the GP semi-char was higher than those of the other two semi-chars: The GP torrefaction significantly reduced the tar formation during the biomass gasification compared to Ap and MP torrefactions. Also, the H-2 and CO yields of GP semi-char gasification were much higher than those of AP and MP semi-chars and raw biomass. Thus, the GP torrefaction was the most effective method for the gasification tar reduction and gasification behavior improvement of the biomass among the three torrefaction methods studied in this work.