A perturbation method is used to evaluate the energy levels and oscillator strengths of sodium atoms (m=-2,π2=+)in a strong magnetic field. The main features of the calculated spectra which lie in the strong-field-mixing regime agree well with the corresponding experimental results. Besides the conventional quasi-Landau resonance with spacing equal to 1.5?ωc (ωc is the electron cyclotron frequency) near the zero field ionization limit, a series of resonance spacings are found and analysed using the zero order energy formula and the Fourier transform technique. The values of these spacings are in consistent with other theoretical results. Based on the perturbation method, a quantum mechanical explanation for the spacings is given. These resonance spacings are independent of the applied exernal magnetic field.