In-situ gasification chemical looping combustion (iG-CLC) depends on the solid fuel gasification rate and the contact between gasification products and oxygen carriers. In this work, a three-dimensional simulation is carried out to investigate the iG-CLC performance of biomass in a fluidized bed reactor by means of the multi-fluid model with the bubble-based bi-disperse drag model to consider the bubble effect on the interphase drag force. The model can give a reasonable prediction on the experimental results. The result reveals that an increase of operating pressure of 0.2 MPa can promote the CO2 yield by 5%, whereas the change of the feed port height from the reactor bottom also greatly influences the outlet gas compositions. (C) 2019 Elsevier Ltd. All rights reserved.