Abstract: According to the need for the wireless sensor network applications in ubiquitous computing environment, a lightweight wireless sensor network OS kernel named uKernel was designed. The improvement of its key techniques especially the task state machine in conventional design procedures was discussed. Based on the conventional embedded RTOS design and energy-saving requirement, the conventional task state machine was improved by way of state decomposition to enable the uKernel to have an energy management mechanism and become a high-efficiency wireless sensor network OS kernel by combining it with corresponding energy-saving algorithm. An experiment was designed to test and verify the effectiveness of energy saving acquired by uKernel.