Abstract: The detected composite foundation's bearing capacity is actually very different from the designed value.And the influencing factors in selecting the bearing capacity of foundation are analyzed in association with engineering geological condition,foundation treatment situation,detection methods.The chief factors analyzed by practical examples include the following aspects: designed parameters values of pile are low,mechanical property of foundation's soil hasn't full utilized and safety stock designed is high.Variable water capacities of the soil between piles are also have effects to some extent.