In this study, a new blood pressure measuring system was proposed and implemented. An additional small-cuff was placed on the center of a inner cuff to measure morphological signals and new oscillometric ratio. The proposed BP-measuring system is composed of an external cuff, an inner cuff and a small-cuff. Oscillation signal from small-cuff is interpolated with 7th-order fitting polynomials and SBP, DBP ratio were 22.2% and 87.7%. Experimental data were gathered from 20 volunteers ($25{pm}4$ years) and arterial blood pressure values were compared with auscultation, sphygmomanometers, small-cuff and inner-cuff. As a result, the difference in systolic BP between auscultation and the small-cuff was 1.93(${pm}1.28$) mmHg, and the inner-cuff was 4.53(${pm}4.39$) mmHg, and sphygmomanometer was 6.68(${pm}3.99$) mmHg, and the corresponding difference in diastolic BP was 2.50(${pm}2.04$) mmHg, 3.50(${pm}3.19$) mmHg, 7.35(${pm}5.62$), respectively.