Abstract: Objective To explore the normal range of intra-abdominal pressure (IAP) using direct measurement, and discuss the relationship between ascites quantitation and intra-abdominal pressure. Methods A prospective cohort study was conducted. We acquire the normal range of IAP in patients without ascites using direct measurement. Meanwhile, we compared the IAP of ascites group with non-ascites group. Then, we injected different volume of normal saline containing chemotherapeutics drugs into the abdominal cavity of non-ascites, monitor the change of IAP, and found the relationship between them. Results ① The 95% confidence interval of the IAP measuring by direct measurement in non-ascites was 4.99-6.11 mm Hg (1 mm Hg=0.133 kPa). ②The IAP of non-ascites was significant lower than ascites group (t=-2.188, P=0.031). ③A significant linear correlation was observed between the volume of normal saline and IAP (R=0.113, t=5.206, P<0.01), the regression equation was Y=7.651X+1.491 (P<0.01). ④The range of IAP after injecting normal saline was 4-19 mm Hg. Among them, there were 52 between 12 and 15 mm Hg and 5 between 16 and 20 mm Hg. There were no patients between 21 and 25 mm Hg and >25 mm Hg. All the patients had no organ dysfunction or organ failure. Conclusion The normal range of IAP measuring by direct measurement is 4.99-6.11 mm Hg, which different from Kron technique in numerical, more studies are needed to explore the relation between them. An increase in ascites can lead the increase in IAP, and there is a linear correlation between them, so we should worry about intra abdominal hypertension (IAH) or abdominal compartment syndrome (ACS) when increase in ascites. The happen of ACS has relationship with the duration of high pressure caused by ascites, so reduce IAP timely has important significance in precention an treatment ACS.