Antihypertensive treatments are inadequate for many hypertensive patients. In these patients, technologies for continuous and comprehensive analysis of the cardiovascular system based on non-invasive measurements of blood pressure, blood flow, and peripheral vascular resistance are desirable. Tonometry and Doppler methods are non-invasive and continuous sensing methods for blood pressure and blood flow, respectively. However, simultaneous measurements of pressure pulse wave by tonometry and blood flow by Doppler method on the same vessel or nearby vessels are difficult, because of the mechanical occlusion of the vessel by the tonometry sensor. This study examined the relationship between pulse pressure and blood flow at the hold-down pressure (HDP) for measuring pressure pulse wave at the radial artery. We quantified the influence on tonometry and blood flow based on the experimental data and determined the optimal HDP that caused no interference between tonometry and Doppler method. The results indicate that the detected pressure pulse wave represents the blood pressure under the optimal HDP, and that the proposed method is capable of sensing blood pressure and blood flow continuously. This proposed method for detecting unexpected fluctuations in blood pressure and its mechanism may contribute to the treatment of cardiovascular disease.