To understand the changes of cardiovascular functions in the initial stage of space flight, the changes in 19 healthy young men during 2.5h head down tilt (HDT) (15 degrees) were observed with CF-II cardiovascular function detecting and diagnosing equipment. The blood pressure and sphygmogram of left radial arterial were recorded in sedentary condition and at 10th, 30th, 60th, 90th, 120th and 140th minute of HDT. The results showed that changes of cardiovascular indices during HDT can be divided into acute regulation stage (< 1h) and the regulation stage (1-2.5 h); circulatory blood volume, stroke volume and cardiac output were increased, while heart rate, pre and after load of the heart, CVP, coronary circulatory function, blood pressure and systemic vascular resistance were decreased; the vagus feedback index increased and the regulation function of vasscule decreased. Most of the changes of cardiovascular indices as reflected in the sphygmogram are in consistent with the reported result in space flight or simulated micro-G, so the sphygmogram method might be applied to space medical research.