Similarity Indexing is very important for content-based retrieval on large multimedia databases, and the “tightness” of data set envelope is a factor that influences the performance of index. For equidistant envelope (bounding sphere), calculation of envelope is somewhat difficult because of the complexity of direct computation in high dimension space. In this paper we summarize the envelope used in similarity indexing structures, and discuss the envelope parameter calculation problem. We improved the γ -spatial search algorithm proposed by R. Kuniawati and J.S.Jin for equidistant envelope parameter calculation, and apply it to various distance spaces. Basic thoughts and theorem are provided in the paper, also with algorithm implementation.