A method for interferometric phase's demodulation with a discrete Hilbert transform is proposed. A Hilbert transform demodulated phase principle is represented and the phase information of aspheric surface is evaluated only one interferogram. The sine and cosine components are calculated from a single interference signal. Then wavefront reconstruction is achieved using Zernike polynomical fitting. In addition, the phase-extraction algorithm, error correction and some applications to the measurement of the surface shape are discussed. On-line measurements to aspheric surface are realized. Several experiments showed the accuracy of the measurement to be λ/10 ( RMS).