The measurement of temperature at the heated point is very important and difficult for the treatmentof tumor using HIFU( High intensity focused ultrasound). According to the theory that the gray scale value va-ries with the ultrasound transmitting through different tissues at different temperatures, a set of experiment e-quipment was designed to describe the temperature field in tissues by using the characteristics of the ultrasonicimage, and an experiment was carried out with fresh liver and muscle tissues of pigs in a temperature arrange of26 ℃ to 64 ℃. The statistical curve of the experiment demonstrates: ( 1 ) The gray scales vary in accordancewith the changes in the temperature of tissue and it is feasible to measure the temperature at the heated point bymaking use of the gray scale variations; (2) Non-linearity is the characteristics of temperature changes and thegray scale of tissues at different temperature phases. Moreover, the gray scale varies from up to down phase atthe same temperature phase; ( 3 ) The gray scale for the same temperature range varies with different tissues. Anexperimented formula is proposed for the measurement of fresh liver and muscle tissues of pigs.