This paper introduces a new concept—space equalization into mutual coupling calibration of digital beamforming (DBF) array. Based on the concept, combined optimization method (COM) is developed to minimize element pattern errors in specified narrow angle and keep global errors being suboptimum. By constructing the cost function of COM properly, the complete equations are derived for the calculation of calibration matrix. Experimental results show that COM calibrates element errors efficiently in constrained narrow space and eliminates mutual coupling errors and channel gain and phase errors in a broad angle region.