Traditionally, network protocols are designed based on the assumptions that network is powered by small batteries with scarce energy supply. However, emerging energy replenishment technologies such as ambient energy harvesting, wireless energy transferring, etc., provide alternatives to address the energy constraint problem but also introduce new challenges (e.g., energy heterogeneity). Been the core to achieve network sustainability, novel network protocols shall be designed to better exploit energy availabilities and tackle new challenges or issues exposed by emerging energy replenishment technologies. In this dissertation, we study how to build a more sustainable sensor network via network protocol innovation. Specifically, the study is conducted in four directions. First of all, we study how to improve energy utilization efficiency on individual sensor nodes as a foundation to improve the network sustainability. Secondly, we study how to prolong the network lifetime as a whole through dynamically and collaboratively tuning MAC layer operational parameters between neighboring nodes. Thirdly, we study the cross-layer design technique and propose a holistic routing and MAC protocol to further prolong the network lifetime. Fourthly, with given sensing coverage constraints, we jointly optimize the routing and sensing behaviors to further improve the network sustainability.