The ultrasonic wave properties of a mixed solution of trioxane and dichloroethane have been studied. A high- precision ultrasonic wave instrument controlled by a personal computer is used to precisely measure the ultrasonic flight- time under the conditions of concentrations 0-48% and temperatures 0-40℃. This paper also calculates the relationships between ultrasonic flight- time
temperature and concentration of trioxane in dichloroethane
which provide the basis for on- line concentration measurement of a mixed solution of trioxane and dichloroethane by ultrasonic method.