To solve the problem of estimating the number of sources when receiving signals with array antennas, a method of estimating the number of sources based on improved quadratic diagonal loading of eigenvalues is proposed. The method comprises the following steps of: carrying out eigenvalue decomposition on an antenna array observation signal covariance matrix; carrying out primary diagonal loading on an eigenvalue, wherein the diagonal loading quantity is taken as the geometric mean value of all eigenvalues, and adding an original eigenvalue and a diagonal loading value to replace the original eigenvalue; For the eigenvalues after the first diagonal loading, the diagonal loading amount of the eigenvalues is recalculated, and the secondary diagonal loading is carried out on the eigenvalues after the first diagonal loading, so that the loaded eigenvalues meet the condition that the ratio of the maximum to the minimum of the noise eigenvalues does not exceed 2. On this basis, the information theory criterion method and the random matrix theory method are used to estimate the number of information sources. The simulation results show that the proposed method is feasible.