Applying the direct simulation Monte Carlo (DSMC) method developed for the cold atom system,we explore the possibility of a high-efficiency sympathetic cooling process between 87 Rb and 40K without gravitational force in an optical trap.The relation between the pre-cooling of Bosons and the sympathetic cooling efficiency is also studied.We find that the absence of gravitational force is beneficial to the process of sympathetic cooling.Furthermore,an inefficient pre-cooling process will in fact hamper the creation of Fermi degenerate gases.This suggests the advantages of sympathetic cooling in microgravity.