A pot experiment with thirty soybean (Glycine max) genotypes differing in root architecture was conducted to investigate the effects of soil phosphorus (P) availability on the colonization of arbuscular mycorrhizae (AM) fungus (Glomus mosseae) as well as the relationships of the colonization with the root architecture and P efficiency of soybean. The results indicated that soil P availability had significant effects on the colonization of G. mosseae. Under low P condition, the AM had a higher infection rate and contributed more to the P uptake by soybean; while under high P condition, it was in adverse. There was a significant interaction between soybean genotypes and soil P availability on the colonization of G. mosseae. Under low P condition, the soybean genotypes with intermediate and deep root architectures had the highest infection rate of AM, but on the contrary, no significant correlation was observed between root architecture and AM colonization under high-P condition. In general, P-efficient soybean genotypes had better root architecture or higher AM colonization, indicating that a complementary relationship between root architecture and AM colonization was existed on their contribution to soybean P efficiency.