The inverse operation of the extended Nijboer-Zernike (NZ) method is applied to acquire the laser beam characteristics. Two images at the locations before and behind the focal plane are used to calculate the amplitude and phase of wavefront at pupil plane of laser beam. The laser beam quality factor M2, the beam width, the divergence, and the Rayleigh range are obtained. The experimental system is established which meets the accuracy requirement. Two actual tests of a He-Ne laser are carried out in different days. The test result of wavefront is compared with that of the phase diversity method and the test results of beam characteristics are compared with that of M2-200s-FW beam analyzer, which shows that the proposed method is reasonable. The stability and reliability of the established system is verified by comparison of the tests in different days.