Abstract: Wireless broadcast environment always affects the transmission quality in wireless sensor networks. In order to improve the SNR and communication rate, an opportunistic scheduling algorithm is adopted to schedule the sensor nodes which are in the good channel states. Multiple antennas are equipped at central node, the other nodes are equipped with single antenna to save energy and volume, which is a multiple input and single output multi-user system. The communication is divided into two stages:at first, the random unitary beamforming is generated by multi-antennas at the pilot stage; secondly, after receiving the pilot information, the sensor node determines whether to enter the communication state according to the preset threshold and then selects the corresponding random beam. The properly truncated threshold is given by Monte Carlo method through communication rate comparison under different situations. The results shows that the SNR and communication rate are both improved by the opportunistic scheduling.