Foam sclerotherapy is one of the major therapies for varicose veins in lower limbs. It is important to know the influence factor of foam stability which is beneficial to curative effect. The present experiment explored influence of 9 kinds of driving speed on foam stability when using the method of Tessari. Syringes of 5 mL were chosen to do this experiment which was carried out at the liquid gas ratio of 1:4 and the environment temperature of 20℃. A home-made automatic sclerosing foam preparation equipment was used to prepare the foam. A camera recorded the entire process of foam decay. And foam stability indexes which includes drainage time, half-life, foam half-life volume and the drainage rate curve, were analyzed. The results showed that when driving speed ranged from 100 mm/s to 275 mm/s, foam drainage time and the half-life showed a trend of rising. When the driving velocity was greater than 275 mm/s, the foam drainage time and half-life time reduced a little. The largest drainage time and the half-life differences were 340.0% and 118.8% compared to their minimum value. Meanwhile the pressure increased with the increase of driving speed, so that the solubility of carbon dioxide increased and the foam half-life volume decreased with the increase of the driving speed. It can be concluded that when using the method of Tessari to prepare sclerosing foam, driving speed has a significant effect on its stability. With driving speed increasing, foam decay mechanism changes from gas diffusion to liquid drainage as the main function, so the foam stability increased at first and then decreased later. The foam is relatively more stable at the speed of 275 mm/s, which could be considered as the best driving speed.