During the plasma discharge in HL-2A, the magnetic field at the plasma boundary is computed using currents filaments code. The Shafranov integrals S1，S2 and S3 are deduced; the poloidal beta, internal inductance, the horizontal position of the magnetic axis Rm and the plasma energy Wdia are calculated; the current center of plasma (Rc,Zc)is computed with the current moments. The real time determination of these quantities is of significance for understanding and adjusting the HL-2A discharge in time, and for improving plasma performance.