In this paper, we proposed the regression model which could estimate unspecified people's systolic blood pressure (SBP) conveniently and continuously and checked its accuracy through clinical experiments. The method for estimating each individual SBP by using only pulse transit time (PTT) has been studied, but it is difficult to estimate unspecified people's SBP with the method using only PTT. Thus we researched several physical characteristic parameters which might affect blood pressure (BP) with the standard that we can measure them easily and conveniently, chose valid physical characteristic parameters through a clinical testing and correlation analysis, and made the regression model using PTT and valid physical characteristic parameters for estimating unspecified people's SBP. Comparing the result of the proposed method with American National Standards Institute of the Association of the Advancement of Medical Instrument (ANSI/AAMI), we know that the proposed regression model gives an acceptable result.