This paper describes objects by Riemannian manifolds and creates Voronoi diagrams based on charts. Difficulties in studying Voronoi diagrams for Riemannian manifolds are discussed. A theorem in existence is given, which demonstrates the present condition of Voronoi diagrams for Riemannian manifolds in a chart. According to the idea and theorem, this paper describes the algorithm of creating charts for two-dimensional Riemannian manifolds and presents the definitions of transition and blend functions. Finally, the algorithm of creating Voronoi diagrams based on charts is given, and some examples are provided.