Coverage capacity analysis of satellites constellation is the basis of satellite system design and performance evaluation, which is essential in the application of satellite technology. A characteristic area based method for continuous coverage analysis is proposed in this paper. The trajectory characteristics of the Walker constellation are first analyzed. The Earth's surface is partitioned into a group of characteristic areas, and the characteristic distance theory is defined and proposed accordingly. On this basis, the formulations of the characteristic point of each characteristic area and the corresponding characteristic distance with all different situations can be analytically obtained. Additionally, sufficient and necessary conditions for continuous coverage are given accordingly. The complex continuous coverage problem can be converted to the analysis of the relations between the critical geocentric angle of the satellite coverage range and the characteristic distance. Computational results indicate the effectiveness of the proposed method and reveal the feasibility in instructing the constellation design.