The reconstructed image is simply seen as the magnified image of an ob ject in digital holographic microscopy (DHM),and hence resulting in the thought that the longitudinal dimension of the reconstructed image is misunderstood as that of the magnified image.For correctly calculating the longitudinal dimensio n of the reconstructed image,the relationship between the lateral and longitudi nal dimension of the reconstructed images is presented in this paper.According to the optical diffraction theory,the theoretical analysis based on the lateral and longitudinal dimension of the reconstructed image is performed to obtain th e relationship.The results demonstrated that the longitudinal dimension of the reconstructed image is not magnified.the lateral dimension of the reconstructed image is identical with the magnified image,which is magnified by M β-fold.Th en,a phase micro-hole arrays etched in quartz glass is used as a sample.The e x periments of measuring the micro-hole arrays in different lateral magnification s (Mβ1=20.29,Mβ2=17.51and M β3=15.3) are performed to compare the dimension of the reconstructed images.The experimental results demonstrated that the longi tudinal dimensions of the three reconstructed images are approximately equal to 570nm,which are not affected by magnification.Whereas,the lateral dimensions of the corresponding reconstructed and magnified images are equal approximately, the max lateral different value is 0.58μm.Moreover,the lateral dimension of the reconstructed image is magnified by Mβ-fold,the longitudinal dimension of the reconstructed image is equal to the longitudinal dimension of the sample,an d which can be calculated by the optical path difference between the object and its surrounding medium.This analysis can provide guarantee for correctly calcul ating the dimension of the reconstructed image in DHM.