Abstract: In order to overcome the deficiencies of embedded particles of microbial fertilizers with the single material and to further improve comprehensive performances of them, the sodium alginate (SA) with polyvinyl alcohol (PVA) and appropriate auxiliary materials was used as main embedding materials in this study. The immobilization was studied by embedding the composite bacteria including rhizobia, phosphate and potassium dissolving bacteria into some small spherical particles. The embedding operation and grain comprehensive performances were acted as indexes in this study. The optimum embedding material concentrations and ratios are SA 3.0%PVA (2.5%3.0%), and auxiliary materials (SiO2 4.0%CaCO3 0.3%). Under the conditions, operability and sphericity are both better, the embedded particles are in regular spheres which diameters are from 3mm to 4mm, mechanical strengths are from 53.4g/g to 59.6g/g , and the embedded rates of bacteria are from 91.4% to 94.3%. The number of viable bacteria in particles reaches 1011cfu/g which is increased 500 times more than that of fresh embedded particles after 72h proliferation culture, and the releasing rate of viable bacteria is more than 90% to total viable bacteria in particles.