Understanding the flame structure for different combustion in industries has drawn the increasing attention around the world.Particularly,for increasing the recent interest of using the hydrogen fuelled vehicles in recent world,structural analysis of flame in combustion chamber has attracted the attention of researchers.However,the high flame temperature and strong flame emissions increase the experimental difficulties,especially,in all kinds of intrusive measurement systems for determining the flame structures and flame temperatures.Therefore,a non-intrusive laser interferometer technique based on Shack-Hartmann optical system has been proposed to measure the thermal characteristic of a flame structure.In the present study,a low-stretched diffusion flame of methanol burner has been used.Shack-Hartmann optical system is a type of wave front sensor.It is commonly used in adaptive optical systems.It consists of an array of lenses to focus the image onto a photon sensor (photo-detector) at the focal plane and measures the wave front tilt.The major objective of the present study is to develop a laser interferometer measurement technique for analyzing the flame structure and its temperature propagation by measuring the density gradient of the flame.Optical interferometer technique is a potential candidate for the non-invasive measurement.In the present paper,a novel method for the measurement of density gradient in flame by using Shack-Hartmann optical system is proposed.A collimated laser beam that has been passed through the flame is tilted due to the density gradient inside the flame.A CCD camera (CCD photo sensor) has been used to observe the wave front tilts at the focal plane. Understanding the flame structure for different combustion in industries has drawn the increasing attention around the world. Particularly, for increasing the recent interest of using the hydrogen fuelled vehicles in recent world, structural analysis of flame in combustion chambers has attracted the attention of researchers .However , the high flame temperature and strong flame emissions increase the experimental difficulties, especially, in all kinds of intrusive measurement systems for determining the flame structures and flame temperatures. Beforefore, a non-intrusive laser interferometer technique based on Shack-Hartmann optical system has been proposed to measure the thermal characteristic of a flame structure. In the present study, a low-stretched diffusion flame of methanol burner has been used. Shack-Hartmann optical system is a type of wave front sensor. It is commonly used in adaptive optical systems .It consists of an array of lenses to focus the image onto a photon sensor (photo-detector) a t the focal plane and measures the wave front tilt. major object of the present study is to develop a laser interferometer measurement technique for analyzing the flame structure and its temperature propagation by measuring the density gradient of the flame. candidate for the non-invasive measurement. In the present paper, a novel method for the measurement of density gradient in flame by using Shack-Hartmann optical system is proposed. A collimated laser beam that has been passed through the flame is tilted due to the density gradient inside the flame. A CCD camera (CCD photo sensor) has been used to observe the wave front tilts at the focal plane.