Abstract: Temperature of a given point near focal region and the size of focal region were measured to study the effect of blood vessel on high intensity focused ultrasound focal region.Blood vessel location and blood flow velocity were varied and the thermocouple probe was inserted vertically to the sound axis into the tissue phantom.After experiment,the size of focal region was calculated by Matlab.Temperature was getting higher and the focal region wass getting bigger when focus was far from blood vessel.The temperature when there was no blood flow near the focal region obviously lower than that when there was blood flow.But when the blood flow velocity was varied,the change of temperature and the size of focal region was not obvious.The blood vessel location and blood flow velocity have effect on temperature distribution of focal region for high intensity focused ultrasound,and blood vessel should be considered when the focal region was close to blood vessel in the clinical treatment.