The digital holographic measurement method and the diffraction propagation algorithm of variable sampling interval were proposed to realize the fine measurement of the focal length and focal spot of the photon sieve. The bifocal photon sieve and its theoretical focal spot distribution were presented. The double-exposure off-axis holographic method was used to obtain the complex amplitude distribution of the light field at the CCD. Based on the light field, the focusing field characteristics of bifocal photon sieves with higher resolution were obtained through the diffraction propagation algorithm of variable sampling interval.The resolution of the focal spot is about 10times that of the direct measurement by CCD. The focal length is equal to the sum of the two distances obtained by the autofocus algorithm and the intensity maximum scanning method respectively. The experimental results show that the deviations between the measured bifocal lengths and the designed focal lengths are 0.53% and 0.37% ,respectively. Compared with the full-width at half-maximum of Greek-ladder photon sieve as required, the measured width of the two focal spots is accurate enough with error of 2.86% and 1.86%, respectively. The measurement method proposed in this paper can be widely applied to the measurement and performance analysis of other diffractive lens focusing characteristics besides the performance testing of photon sieves.