Considering that there are many uncertain factors in the construction process of power transmission and transformation projects and the cost calculation tends to be stationary, a real-time dynamic calculation model of transmission and transformation project cost based on blockchain data security mechanism is established in this paper. The model accomplishes the accuracy and efficiency of the calculation results of power transmission and transformation project cost. First of all, the blockchain trusted data exchange technology is used as the underlying model. Utilizing the decentralized characteristic of blockchain, the immutable characteristic of the chain data and other characteristics, the architecture system of data uploading, interaction, storage and calculation in power transmission and transformation projects is constructed. Secondly, particle swarm optimization algorithm is used to optimize the parameters of RBF neural network and the prediction calculation model of power transmission and transformation project cost data is constructed. Finally, Jaccard distance is used to correct the calculation results and react the error while optimizing the model. The model is verified to be advanced and feasible by simulation examples.