Dynamic control of the projected cost of building groups in post-earthquake restoration and construction stages is more changeable than during other stages. Pre-control systems with high precision and flexibility are needed to ensure that there is no deviation in projected cost. In this paper, a dynamic pre-control system of projected cost in the restoration and construction stages of a post-earthquake building group was designed. Relevant personnel entered the system interface through the user login module. In the project information management module of the system, an improved genetic algorithm was used to develop the projected repair cost model of the building group as part of the overall system design. Experimental results showed that the dynamic cost pre-control system, based on an improved genetic algorithm, effectively realized dynamic cost pre-control in the restoration and construction stage of the post-earthquake buildings. With increasing number of cost samples, the error rate gradually decreased; moreover, the flexibility of pre-control was always >95%, and the use practicability was only 0.04. This system can provide a reference for cost control of post-earthquake construction.