The invention discloses a project cost management system based on big data. The system comprises a personnel numbering module, a data statistics module, a data analysis module, a region division module, a soil specific gravity detection module, a soil specific gravity analysis module, a compactness detection module, a compactness analysis module, an analysis server, a project cost management center, a display terminal and a storage database. According to the method, the engineering construction difficulty evaluation coefficient estimated by each engineering cost person is counted, the averageengineering construction difficulty evaluation coefficient estimated by each engineering cost person is calculated, the soil texture proportion of each foundation subarea in a to-be-constructed building is detected, the soil texture type of the to-be-constructed building area is analyzed, comparison is conducted to obtain a soil compactness comparison difference value of each foundation subarea, an engineering construction difficulty evaluation coefficient estimated by the system is calculated, and a comprehensive engineering construction difficulty influence coefficient of the to-be-constructed building is calculated according to the weight ratio, thereby improving the estimation accuracy and reasonability of the construction engineering cost.