Clustering is an effective self-organization approach in wireless sensor networks. LEACH--a representative distributed clustering scheme has been considered an effective model to offer energy-efficient communication for sensor networks. However, its randomness may result in faster death of some nodes i.e. shorten system life. In this letter, we first analyze the reasons why the uncertainty in LEACH degrades system life, and then present a distributed clustering algorithm based on an adaptive backoff strategy. Simulation experiments illustrate that our algorithm is able to significantly prolong system life compared with LEACH.