With the large-scale integration of photovoltaic (PV) into the distribution network, energy storage (ES), as a flexible and economically controllable resource, becomes an important choice of investment for distribution network planning to smooth out the fluctuation of PV generation and improve the economic efficiency of distribution network operation. The traditional methods identify the optimal allocation ratio of PV and ES in distribution network planning and analyze the economic benefits of distribution network planning by solving a large number of optimal distribution network planning problems. However, these methods are computationally inefficient and cannot explicitly quantify the impact of ES capacity on the overall economic efficiency, making it difficult to guide distribution network planning. Therefore, an explicit characterization and quantitative analysis method for the optimal allocation ratio of photovoltaic and energy storage for distribution network planning is proposed. First, a distribution network planning model is constructed, which contains constraints of PV generation and physical operating characteristics of ES integrated into the distribution network and aims at the highest overall economic efficiency of PV and ES planning in the distribution network; on the basis of this, the model is converted into convex by pre-solving method. Then, based on the multi-parameter planning method with PV capacity as the planning parameter, the analytical expressions between the optimal planning capacity of ES and the PV capacity of distribution network, the cost of distribution network planning and the PV capacity of distribution network, are constructed. Finally, based on the analytical expressions, the optimal ES capacity under different PV capacities and the mechanism of optimal allocation ratio of PV and ES affecting the economic efficiency of distribution network planning are analyzed, which can assist the establishment of distribution network planning schemes. The results of the case study in PJM 5-bus system and IEEE 141-bus system verify the effectiveness of the proposed method.