针对数字全息中目标焦平面的精确定位问题，在对边缘灰度梯度法进行补充的基础上，提出了全局灰度梯度法，进而结合上述两种方法得到了综合灰度梯度法。利用模拟粒子数字全息图进行了大量的实验研究对比，讨论了边缘灰梯度法和全局灰梯度法各自的最佳适用范围。前者适用于大尺寸粒子和近距离情况，而后者在小尺寸粒子和大物距的情况下会得到比较好的焦平面位置。将综合灰度梯度法具体应用于不同条件下的标准粒子靶面目标，结果均能有效地获得不同粒子的高精度焦平面位置。

To accurately locate the focal plane of object in digital holography, the overall sharpness (OS) method, which is the supplement of the edge-sharpness (ES) method, is presented. By combining above methods, the integrated gray-level gradient method is obtained. The criterion with ES is confirmed to be appropriate for large particles or small object distance. In contrast, the criterion with OS is determined to be appropriate for small particles or large object distance. The conditions of above criteria are discussed by using numerical simulation holograms of particles. At last, the integrated gray-level gradient method is applied to the real holograms of dot array target and calibration target. The experimental results demonstrate that this method can effectively extract the focal plane of particle.