The power grid engineering data varies frequently due to the complex geographical location, long span distance and long cycle, and the external environment, market and human stochastic factors, which makes the cost control of power grid engineering difficult. The data chain construction of power grid engineering based on blockchain technology can realize the management of data integrity, process supervision, and traceability. The probabilistic analysis model of power grid engineering data is established, and the sensitivity calculation model of the different random factors influence on the engineering data changes is studied. Based on the improved differential evolution algorithm, the optimal risk level of power grid engineering is calculated, and a differentiated risk management process of power grid engineering cost data based on blockchain is proposed. The analysis of engineering examples shows that the proposed method can improve the reliability of the cost data, proactively respond to the risk of cost changes, and realize the differentiated management of different engineering data.