According to refractive indexes of nanomaterials （less than 1.4） and the AM0 solar spectrum, antireflection coatings of space Si solar cells are designed and analyzed. For double-layer and tri-layer antireflection coatings fabricated by normal and nanometer materials, the optimal parameters of coatings and reflection coefficient curves are obtained. The double-layer and tri-layer new nano antireflection coatings are optimized, and have better antireflection compared with those fabricated using the normal materials. It is interesting that, after optimizing, the minimal weighted reflectance of the new nano antireflection coatings is 15% and 24.5% less than that of the normal antireflection coatings for the double-layers and the tri-layers, respectively.