Abstract: Spherical distance (Angular separation) calculation is commonly using in Astronomy and Geography. It is the foundation of object detecting, data query and cross-matching. The spherical distance can be computed by Spherical Geometry method, and people have deduced many formulas. But the precision of computer is limited, due to rounding error in the numerical computation. This article will inspect several widely used formulas, test and compare their results, and discuss their advantage and disadvantage. In addition, this article will demonstrate how to do distance calculation on several astronomical packages and databases. The purpose of this article is to help astronomers to find the suitable method to do their calculation.