The invention belongs to the technical field of cognitive radio, relates to a spectrum sensing method for multiple antennas. When it is sensed that the user has multiple space related antennas, a multi-antenna spectrum sensing problem is equivalent to a Ljung-Box (LB) test problem. It is well known that one complex multiplication involves four real number multiplication and two real number addition. In the method, a received signal is converted from a complex number field to a real number field, so that the calculation complexity is reduced effectively.