In order to solve the problem of discoloration, melting and falling off of artificial speckles when the conventional digital image correlation method is applied to thermal strain measurement under high temperature conditions, the laser speckle was used as the characteristic texture method of the digital image correlation method. The correlation of speckle images before and after temperature change to measure metal thermal strain was calculated, experiments of heating specimens in a non-vacuum environment were carried out, the artificial speckle and laser tests on aluminum and tungsten specimens in a tubular heating furnace respectively vacuum heating experimental comparison of speckle were conducted.The corresponding speckle images were obtained and the mean strain curve data were calculated. The results show that in the non-vacuum environment, the laser speckle image jitters greatly due to the disturbance of heat flow, and the measured thermal strain curve has large interference noise. The thermal strain of aluminum with the temperature increases from room temperature to 450 ℃ and the thermal strain of tungsten with the temperature increases from room temperature to 800 ℃ is respectively consistent with the artificial speckle results. This study shows that the laser speckle digital image correlation method can effectively measure the dynamic thermal strain of the metal wall under the conditions of high vacuum and high heat flow similar to the fusion reactor divertor, which provides a new idea for the damage diagnosis of the first wall material of the fusion reactor divertor.