Abstract: This article fully investigates the stress ratio of pile and soil and the bearing-deformation mechanism of composite foundation with cement mixing piles whose pile spacing becomes larger by means of the static load test and pile-soil stress testing.Because of bringing the lateral friction of mixing piles into play for composite foundation of pile space s=(2.57～2.64)d,the stress of soil between piles cannot overlap,which makes the composite foundation form a reinforced cushion to diffuse additional stress effectively,so it obviously reduces the settlement of composite foundation.