In particle digital holography, the process of determing focal distance is cumbersome and complex using traditional numerical reconstruction methods. Based on HilbertHuang transform, a method for detecting axial position of particle from inline digital hologram is presented. The radial intensity distribution of single particle hologram is transformed by empirical mode decomposition which results in several intrinsic mode functions. The particle position can be determined by using liner regression of the first intrinsic mode function′s Hilbert spectrum. The validity and reliability are demonstrated by the theoretical simulation and experiments. Since it does not need to reconstruct the hologram, this method is expected to be used in real time digital particle hologram analysis.