As the flexibility needs of new power systems with a high share of new energy sources increase, it is important to develop a flexibility resource market operation mechanism to balance the volatility and uncertainty of large-scale new energy output in real time. To this end, a wind-photovoltaic-thermal-hydrogen coordinated planning method based on a demand proportional allocation mechanism (DPAM) is proposed in the paper. Firstly, a three-phase coordinated operation strategy for wind and photovoltaic systems with hydrogen storage is formulated. Inter-station power trading between wind and photovoltaic based on DPAM coordinates the revenues and expenditures of wind and photovoltaic stations. Thermal power and hydrogen storage systems are used to provide operational flexibility, and a fixed-profit-proportional model is used to ensure the stability of hydrogen storage system revenues. Then, integrating the investment decision and operation simulation, power trading costs and flexibility resource regulation costs are incorporated in the optimization objective. A multi-timescale coordinated planning model with wind serving as the primary power source and thermal power and hydrogen storage as the auxiliary power sources is established. Finally, a provincial grid in northeast China is used as an example for analysis. The results show that the proposed methodology can be used for power planning in an economical and environmentally friendly way, reducing flexibility resource requirements and investment costs while incrersing the power utilization of wind and photovoltaic stations.