Abstract: Objective: To investigate the difference and relevance between central venous pressure (CVP) measurement by automatic reading and end-expiratory manual reading and to analyze as well as discuss if they could be substituted by each other Methods: A prospective observational study included 200 critically ill patients who received CVP monitoring and received CVP measurements by automatic reading of monitor system and manual reading at the end of expiration was applied. We compared the difference between these two methods. Results:CVP measurement by automatic reading was significantly positively correlated with the results obtained by end-expiratory manual reading (r=0.905, P<0.001), and patients with difference between two measurements greater than 2 mmHg accounted for 17.0%. ②Of the 123 mechanical ventilated patients, the correlation between two measurements was r=0.915, while of the 77 spontaneous breathing patients, the correlation was r=0.886. The patients with difference between two measurements greater than 2 mmHg accounted for 28.6% (spontaneous breathing) and 9.8% (mechanical ventilation).Of the 177 patients who had sinus rhythm, the correlation between the two measurements was r=0.921, while the correlation was r=0.891 of the 23 arrhythmic patients, patients with difference between two measurements greater than 2 mmHg accounted for 30.4% (arrhythmia) and 15.3% (sinus rhythm). Conclusion: The two measurements correlated well in fully mechanical ventilated patients and the results showed that they could be replaced by each other. But the difference between two methods was greater in spontaneous breathing patients and arrhythmic patients, so we should be alerted when results of automatic reading were applied.