In order to find a systematic approach to aid the creative design of mechanisms, this thesis proposes a unified structural synthesis method for planar kinematic chains and mechanisms with simple and multiple joints, characterized by effectiveness, automation and human-machine interaction, and develops the atlas databases containing all the topological graphs for these kinematic chains and mechanisms with different numbers of links, classified by their structural characteristics. Based on the classified atlas databases, the creative design of several kinds of mechanisms is also conducted to verify the usefulness of the method. The overall structure of the thesis is as follows. (1) In chapter 2, the representation models of planar kinematic chains with simple joints, multiple joints and geared joints are presented and the relationships between these models are revealed. (2) In chapter 3, the relationships of contracted graphs of planar non-fractionated kinematic chains and their link assortment arrays are revealed first. Then a fully-automatic method for the synthesis of the contracted graphs of planar non-fractionated kinematic chains is proposed. With the method, the complete families of non-fractionated contracted graphs and of valid contracted graphs with up to eight basic loops and all possible degrees of freedom are synthesized and obtained for the first time. (3) In chapter 4, a general method is proposed to synthesize planar non-fractionated kinematic chains and mechanisms based on the obtained contracted graphs. The method is fully-automatic and designer-friendly, and planar non-fractionated kinematic chains and mechanisms with up to 19 links are synthesized. Moreover, the classified atlas databases for these kinematic chains and mechanisms are also established. (4) In chapter 5, based on the structure characteristics of fractionated kinematic chains, a general synthesis equation of planar fractionated kinematic chains is proposed first. Then an automatic method is proposed to synthesize planar fractionated kinematic chains by the combination of planar non-fractionated kinematic chains, and the whole family of planar fractionated kinematic chains with up to seven basic loops is synthesized for the first time. (5) In chapter 6, based on the new bicolor topological graph and its inter-convertible characteristics with that of simple joint kinematic chains, an automatic method is proposed to synthesize multiple joint kinematic chains from simple joint kinematic chains and their classified atlas databases. The whole family of multiple joint kinematic chains with up to 16 links is synthesized for the first time and corresponding classified atlas databases are also established. (6) In chapter 7, based on the structural synthesis and classified atlas databases of kinematic chains with simple and multiple joints, a creative design method is proposed to obtain all the feasible mechanisms for a specified task from the topological graphs in the classified atlas databases subject to design constraints. The creative design of road tractors, hydraulic robots and forging manipulators is conducted as examples, and a number of novel mechanisms are obtained for the first time together with the widely used ones.