Abstract: This paper analyzed the common electronic map projection distortion,and proposed a discontinuous change of the standard parallel for map tiles' indexing method based on the equidistant cylindrical projection.This indexing method sets angle deformation at the standard parallel as 0 and reduce the deformation by custom defined standard parallel and changing it automatically.Through computing and comparing the length deformation,angle distortion and area deformation of this method and others,it shows that this method have moderate deformation characteristics and also have good deformation controllability in regional electronic map.Therefore,this indexing method will have a high practical value.