Several acoustic parameters including the pressure coefficient of ultrasonic velocity，temperature coefficients of ultrasonic velocity and the nonlinear acoustic parameter of liquid and supercritical carbon dioxide at different temperatures and pressures were calculated by using data of sound velocity，density，specific heat at constant pressure and bulk coefficient of expansion of carbon dioxide provided by the National Institute of Standards and Technology，USAThe nonlinear acoustical characteristics of liquid and supercritical carbon dioxide were analyzed and summarizedThe nonlinear acoustical characteristics of supercritical carbon dioxide were contrasted with those of liquid carbon dioxide and common organic liquidThe nonlinear acoustical characteristics around the critical angle were analyzed in detailInvestigation indicated that the nonlinear acoustical characteristics of liquid carbon dioxide resembled common organic liquid at normal temperature and normal pressureThe values of pressure coefficient of ultrasonic velocity，temperature coefficients of ultrasonic velocity and the nonlinear acoustic parameter of supercritical carbon dioxide might be positive or negative and the values changed with temperature and pressure regularlyThe higher the pressure and the lower the temperature，the more the nonlinear acoustical characteristics of supercritical carbon dioxide agreed with those of liquid carbon dioxide or common organic liquid at normal temperature and normal pressureNear the critical region，the change of these three parameters with temperature and pressure had a jump between positive and negative maximum.