This paper presents a work-item-based scheduling system that employs MD CAD model, Object Sequencing Matrix (OSM), and Genetic Algorithms (GAs) to generate the time-cost integrated schedule for construction projects. Consisting of MD CAD objects, the MD CAD model ensures the consistency and efficiency of information processing and integration in project planning. In the development of MD CAD model-based scheduling system, the Object Sequencing Matrix (OSM) is adopted to formulate a construction sequence of building components based on the physical relationships between MD CAD objects. Genetic algorithms (GAs) are then applied to optimize the sequence of building components and the assignment of crews. As a result, a feasible time-cost integrated project schedule is developed. In computer implementation, the MD CAD model-based Project Scheduling System (MD-PSS) is presented to verify the feasibility of the proposed approach.