With the increasing lack of allocable spectrum and crowding of ISM (Industrial, Scientific and Medical) bands, the research and application of wireless sensor networks (WSN) will face a major difficulty that acquire usable spectrum. Moreover，purchasing spectrum rights with lots of money is unreasonable under an emphasis on low cost to WSN. Thus an alternate method based on the concept of Cognitive Radio is explored to capturing spectrum for WSN. Two cooperative detection techniques based on energy detection are introduced, with the consideration of channel shadowing or fading. The simulation results show that the proposed energybased cooperative spectrum sensing methods lead to a favorable performance in detection probability, which makes a foundation for exploring usable spectrum for WSN.