Selective low-temperature pyrolysis of microcrystalline cellulose was carried out to produce levoglucosan (LG) and levoglucosenone (LGO) using a fixed bed reactor. The effects of temperature, self-produced bio-char, different catalysts and catalytic pattern on produces yields and selectivities were studied. The results showed the self-catalysis of bio-char increased LGO yield from 0.14 wt% to 1.35 wt% by increasing almost 10 times with reaction feedstock mass increasing 3 times. The maximum LGO selectivity of 77.67% was obtained with H3PO4 catalysts at 270 degrees C. Through comparing different catalysts including H3PO4, H2SO4, Fe-2(SO4)(3) and FePO4, the highest LGO yield of 2.65 wt% was obtained with Fe-2(SO4)(3). Acid catalysts can obviously increase LGO selectivity and in-situ pattern performed better than ex-situ pattern during the pyrolysis for LGO. Finally, the mechanism with bio-char effect for producing LGO and LG from selective pyrolysis of microcrystalline cellulose was proposed.