A phase reconstruction method using a rhombic-Gaussian combined filtering window is proposed in order to solve the problems of susceptibility to noise, spectral leakage, and crosstalk from other order spectra in the extraction of differential phase using conventional filtering windows in quadriwave lateral shearing interference (QLSI) phase reconstruction. By combining a rhombic window on the spectrum plane with a series of two-dimensional Gaussian windows perpendicular to the spectrum plane, the differential phases in two orthogonal directions are extracted from the QLSI interferogram. Finally, the phase to be measured is reconstructed from the two differential phases by a least square based Fourier transform method. Experimental measurements are implemented under a standard sample to compare the proposed rhombic-Gaussian composite window with four conventional filtering windows on the effects of the reconstructed phase in terms of the accuracy of the phase difference, root mean square error (RMSE), and peak-to-valley (PV) error. The results demonstrate that the phase difference of the phase retrieved by the proposed method is closest to the nominal value of the sample, and the RMSE error and PV error of the reconstructed phase are both the minimum, thus effectively improving the quality of phase reconstruction.