Based on the theory of POC and ordered single-opened-chain, a design method for structural synthesis of lower-mobility non-overconstrained parallel mechanisms (PMs) was proposed according to the over-constraint characteristics of independent loops. Firstly, the relationships between POC of mobile platform, POC of kinematic limbs and the number of independent displacement equations of independent loops were analyzed. The existence condition of lower-mobility non-overconstrained PMs was obtained, and the universal method and step for structural synthesis were further proposed. Secondly, the non-overconstrained PMs can be classified into three types of configurations according to different combinations of kinematic limbs and their corresponding constraints on the platform, which showed that the non-overconstrained PMs composed with different types of kinematic limbs had different performances. Finally, the rules of possible kinematic limbs and their assembly modes were illustrated by comparative analysis with a few examples. The research results enriched the analysis theory and methods of non-overconstrained PMs, and laied the foundation for type selection and applications of lower-mobility non-overconstrained PMs.