Digital holographic microscopy plays a key role in micro-fluid measurement,and appears to be a strong contender as the next-generation technology for diagnostics of three-dimensional (3D) particle field. However, various recording parameters, such as the recording distance, the particle size, the wavelength, the size of the CCD chip, the pixel size and the particle concentration, will affect the results of the reconstruction, and may even determine the success or failure of a measurement. In this paper, we numerically investigate the effects of particle concentration and the volume depth on reconstruction efficiency, to evaluate the capability of digital holographic microscopy. Standard particle holograms with all known recording parameters are numerically generated by using a common procedure based on Lorenz-Mie scattering theory. Reconstruction of those holograms are then performed by a wavelet-transform based method. Results show that on the premise that the value of volume depth is 24 μm, the reconstruction efficiency Ep decreases quickly until particle concentration reaches 6.89×105 mm-3, and decreases slowly with the increase of particle concentration from 6.89×105 mm-3 to 55.08×105 mm-3. And on the premise that the value of particle concentration is 13.77×105 mm-3, the reconstruction efficiency Ep decreases linearly with the increase of the volume depth. When shadow density is constant, the variance of the construction efficiency presents a certain regularity. When the volume depth is small, the effect of particle concentration on the reconstruction efficiency becomes larger than one of volume depth, while it comes to a completely opposite result with a larger volume depth.