The shrink-gun from the market has some problems while in operation, such as unstable flame, uneven temperature and noisy…etc, they may cause the package shrink bad, gas wastage and unsafe working environment. By using computer-aided engineering technology, to complete the sample and turn the testing result into numeric and analyze the data to find the appropriate improved design. This research is to use the fluid dynamics, gas combustion theory and computer-aided engineering and to identify the testing method, hand-made fixture and thermal imager tools, by testing lot to retrieve the data of operating hot air gun and improving the sample to be better than the product in the market. To compare the data between marketing shrink-gun and the new shrink-gun, to learn the advantage of this new shrink-gun.