The ultrasonic parameters(velocity and attenuation coefficient) of milk with different fat content were detected at different temperatures.The relationships of fat content and ultrasonic parameters and influence of temperature on these relationships were analyzed.The experimental results showed that changes in fat content had little effect on the ultrasonic velocity,the maximum rate of the changes of velocity was just 0.164% at 39.1℃;the change of velocity / temperature in fat content was slightly bigger,the rate of which was 4.29%;attenuation increased significantly with the increase of fat content,the rate of change of attenuation at 39.1℃ was the largest of 113.2%,while the changes between attenuation / temperature and fat content was 40.4%.These indicated that the changes of attenuation with changes in fat content was the most obvious,and attenuation was little sensitive to temperature.Therefore,the attenuation coefficient is the better indicator for detecting the difference of milk fat content.