With the bamboo fiber and polyolefin as the major raw materials plus small amount of modified processing agent, highly filled bamboo plastic composite pellets were prepared by co-rotating parallel twin screw granulate line and further molded into packaging boxes by injection. The effects of fiber content, resin, lubricant and filler on processing performance and molding cycle and the effects of resin composition and mould temperature on packaging box buckling deformation were studied. The results showed that melt flow rate of the composite experienced a sharp decrease with the increase in bamboo fiber content, and the descent rate slowed down after the content exceeded 50%. Lubricant promoted the flowability of the composite and the complex lubricant brought about a more stable performance. Talcum could improve the melt flow index of the composite better than calcium carbonate. Buckling deformation of the bamboo composite packaging box declined with the increase of polypropylene share in the resin and fluctuated with mould temperature. The best mould temperature for the least buckling deformation was about 50 ℃.