A technique of monitoring the change of blood perfusion utilizing the principle of laser speckle technique combined with CCD imaging method was studied. A laser speckle measurement system of measuring the velocities of blood flow in rat's mesentery was designed in present paper. The parameter and precision of the system was testified by a model experiment. On this basis, the dynamic changes of the velocities of the blood flow in rat's mesentery under different temperatures were measured. Meanwhile, the diameter of blood vessels was measured with CCD camera. With these measurements, changes of blood perfusion by heat were studied. The results indicated that this system and method could be used to monitor the change of blood perfusion effectively. This work provides a new method to measure thermal induced change in blood perfusion of tissue.