Through the assessment 101 limbs of 77 subjects by air plethysmography (AP), we studied the method of AP test and the values of various indices in diagnosis of primary venous insufficiency (PVI). Venous filling index (VFI) was found valuable to quantitate the venous reflux with its value beyond the threshold of 5 ml/sec. It has a potential value to assess the effect of operations on PVI, such as valvuloplasty aiming to abolish venous reflux. Ejection fraction (EF) was found to be abnormal with its value less than 40%. It may be used to evaluate the function of calf pump quantitatively, predict the ulcer formation, and help make a decision of surgery timely. The comprehensive analysis of VFI, EF, RVF (residual volume fraction) and AVP (ambulatory venous pressure) indicated that there seems to be different types of PVI: type 1, low ejection (low EF) high venous reflux (high VFI); type 2, high ejection low venous reflux; type 3, low ejection low venous reflux. This new classification may impose some on the selection of adequate therapies, which will be further investigated.