Objective To explore the relation between the enlargement of orbital volume and the degree of enophthalmos, and that between the enlarged volume of floor together with that of medial wall and the degree of enophthalmos. Methods A total of 17 patients of unilarteral orbital fracture were scanned by MSCT (slice width 0.625mm), who suffered late enophthalmos as a results of combination fracture of the medial wall and floor. The clinical data were collected, and input into a software named MIMICS in order to measure orbital volume, the degree of enophthalmos, the enlarged volume of medial wall, and that of orbital floor. Simple linear correlation and regression were carried out between the enlargement of orbital volume and the degree of enophthalmos. Mutiple linear correlation and regression were carried out between the enlarging volume of floor together with that of medial wall and the degree of enophthalmos. Results The equation of the enlargement of orbital volume (V) and the degree of enophthalmos (E) was E= 0.851 V-0.197 (Pearson r=0.969, P＜0.01, the 95% confidence intervals of 0.732-0.970). The standardized equation between the enlarged volume of floor together with that of medial wall and the degree of enophthalmos was E= 0.690 VF+0.413 VM-0. 086 (setpwise, entry =0.5, removal= 0. 11,P＜0.01 ); Comparing the standardized coefficients of independent variables, the outcome was bF (0.690) ＞ bM(0.413). Conclusion Significant linear correlation between the increment of the orbital volume and the degree of enophthalmos is found that 1.0 ml enlargeement in bony volume causes approximately 0.9 mm of enophthalmos; enlarged volume of floor has more powerful influence on the degree of enophthalmos than enlarged volume of medial wall, the former is 1.56 times of the latter.