High penetration of renewable energy brings seasonal electricity imbalance in the power system and results in considerable energy curtailment. Such large scale curtailed electricity could be used to produce hydrogen via Power-to-Hydrogen (P2H) technology. The introduction of P2H would largely affect the configuration of both power grid and the hydrogen supply chain (HSC). This paper proposes a coordinated planning model of power system generation and transmission (GT) as well as HSC with transportable seasonal hydrogen storage. A co-planning model is put forward to investigate the optimal configuration of infrastructures in the GT-HSC and their coupling during operation. The model is formulated as LP model so that the year-round energy balance of seasonal hydrogen storage with daily resolution could be considered. Case studies on 5-bus PJM system and Northwest China HRP-38 system demonstrate the effectiveness of the proposed model. Results of the case study also illustrate the benefits of incorporating GT with HSC to reduce the renewable energy curtailment and bring down the energy supply cost.