Aiming at the problem of low probability of blind spectrum sensing detection, a two level spectrum sensing algorithm based on correlation coefficient for multi-antenna system is proposed. Firstly, the correlation coefficient is obtained by sampling the covariance matrix of multi-antenna system. Secondly, take the maximum and minimum correlation coefficients as the first detection statistics. Finally, make the seconde detection by reconstructing the new test statistics between the threshold. Monte Carlo simulation shows that in the case of few sampling times, especially in low signal to noise ratio (SNR) conditions, with the increase of the number of users, the detection performance is better. Compared with the traditional double threshold detection, the algorithm does not need to increase the number of sampling time and it saves operation cost.