Influence of residual gas in a laser fusion reactor chamber at the time of pellet injection is discussed, including the lifetime of a cryogenic target, the stall by drag force, the deviation by a crosswind and the lift by spin of the pellet. The pellet is assumed to be injected accurately with designated speed and direction every time. Preliminary results indicate that the vapor pressure in the chamber should be less than 0.1 Torr and the shot-to-shot variation in the wind speed must be less than 1 m/s to deliver the fuel pellet at the firing position with an accuracy of 100 μm.