Planetary centrifugal bioreactors are promising candidates for cell culture platforms since there is no pollution caused by stirring blades. In this work, the fluid structure in a planetary centrifugal bioreactor was investigated using the computational fluid dynamics (CFD) method. The effects of operating conditions on the oxygen transfer rate (OTR), mixing efficiency and shear environment of the bioreactor were studied with the revolution speed (N) ranging from 60 to 160 rpm and the rotation-to-revolution speed ratio (i) from -2 to 1. The results show that the volumetric mass transfer coefficient (kLa), turbulence intensity, volumetric power consumption, and shear stress increase along with the increase of the revolution and rotation speeds. Furthermore, the rotation in the opposite direction to the revolution is beneficial to the performance of the bioreactor. The planetary centrifugal bioreactor has a higher kLa of 50- 200/h and a lower average shear stress of 0.01-0.05 Pa in comparison with conventional stirred tank bioreactors, which makes it suitable for biological culture of oxygen-consuming cells and shear-sensitive cells.