Abstract: Discussing the particularity and diversity of the task of sensor network nodes, the commonly-used real-time operating system SNNEOS (sensor network node embedded operating system) is explored including its structure, management of kernel interruption and communications subsystems, as well as the implementation mechanism of its transfer protocol. As an event-driven, SNNEOS can avoid CPU round-robin and save power. By the real-time kernel and non-real-time kernel interruption, the real-time task is separated from non-real-time one so as to respond to key real-time tasks punctually. To implement SNNEOS easier and clearer, the communication subsystems are processed in layers and each layer provides an individual process.