Biomass　tar　as　a　byproduct　during　the　gasification　process　can　lead　to　many　problems,　such　as　condensation　and　subsequent　plugging　downstream.　However,　the　knowledge　of　the　correlations　between　the　tar　formation　and　conversion　and　the　gas-solid　hydrodynamics　in　fluidized　bed　gasifiers　(FBGs)　is　still　limited　compared　to　other　aspects　of　biomass　gasification.　In　this　study,　a　three-dimensional　comprehensive　model　that　simultaneously　coupled　the　detailed　tar　kinetics　and　the　homo-　and　heterogeneous　kinetics　with　the　multi-phase　particle-in-cell　hydrodynamics　was　constructed　for　a　biomass　FBG.　Numerical　predictions　were　in　very　good　agreement　with　experimental　data.　The　influences　of　the　oxygen　concentration　in　the　gasifying　agent　and　the　biomass　particle　size　distributions　on　the　gasification　process　were　investigated　using　the　comprehensive　model.　Numerical　findings　indicated　that　a　high　oxygen　concentration　of　the　gasifying　agent　reduces　the　nitrogen　dilute　effects　and　increases　the　gasification　temperature,　giving　rise　to　a　low　tar　yield　and　high　gasification　efficiency.　A　small　particle　size　enhances　the　releasing　and　diffusing　rates　of　volatiles　from　biomass　particles,　resulting　in　a　low　tar　yield　and　high　gas　yield　and　gasification　efficiency.　It　is　believed　that　the　comprehensive　model　can　assist　to　explore　the　tar　formation　and　conversion　behaviors　on　the　particle　scale　for　the　biomass　gasification　process.