The invention discloses an opportunity spectrum access method based on a sideband observation information multi-arm tiger machine model. The method comprises the following steps: firstly, aiming at asecondary user access problem under the conditions that cognitive network channel information is unknown and channel perception is imperfect, carrying out detection perception on N channels, and selecting a channel problem suitable for access to be modeled as MABP-SI model; sensing all authorized channels by a secondary user, recording a sensing observation result, updating a probability vector, and recording a channel set which is sensed to be idle; creating a candidate set of spatial probability vector estimated values, and selecting an estimated value of an idle probability vector; judgingwhether the idle channel set is empty or not at the time slot t: if the set is empty, not accessing the secondary user to any channel, and if the set is not empty, selecting k authorized channels withthe maximum coefficient to access; and finally, updating t to t + 1, and circulating. According to the method, the income loss of channel access under the statistical asymptotic condition is reduced,and the method has the advantage of statistical asymptotic effectiveness.