Based on the principle that it is possible to test minuteness displacement and deformation with electronic speckle pattern interferometry (ESPI), the heat reliability of very large scale integration (VLSI) is tested. The speckle pictures of two different CPU under different heat load are obtained experimentally. By using the approximate formula of off-surface displacement. The off-surface displacement values are calculated and the simulation curve of off-surface displacement with heat is plotted. Through analyzing the changes of curve, the heat reliability and the stability of CPU are expressed. Because this test means is fast nondestructive and with high reliability, it can not only fit for heat reliability test of VLSI package, but also for package reliability test of many other electronic and photo-electronic devices.