Objective To find the correlation between the diameter and collapsibility of the inferior vena cava （IVC） and the CVP in patients after cardiovascular surgery. Methods Eighty-four patients after the cardiac valve replacement in Xinqiao hospital were into group. The maximal and minimal transverse diameter(IVCmax and IVCmin) were measured in the two-dimensional long axis view of the IVC，obtained on the midline of the right clavicle midline and axillary line，then the collapsibility of IVC diameter was calculated. While CVP was measured by external jugular vein into superior vena cava catheter. The correlation between IVCmax, IVCmin, collapsibility and CVP were analyzed by Spearman’s and Pearson’s methods in spontaneous or mechanical ventilation condition respectively. Results IVCmax is （1.54±0.45） cm，IVCmin is （1.19±0.45） cm，collapsibility is （24.02±11.52）%, CVP is （9.46±4.02） cmH2O. Either in a spontaneous or mechanical ventilation condition，a negative correlation was observed between IVC collapsibility and CVP （P＜0.01），while there is a positive one between IVC diameter and CVP （P＜0.01）. Conclusion For patients after cardiac valve replacement，both the diameter and the collapsibility of IVC were related to the CVP. Using ultrasound to measure the diameter of IVC，is conducive to the determination of fluid responsiveness.