In order to accurately extract out Moiré fringe deviations, the tunnel-exploring algorithm was proposed, and used to analyze Moiré patterns.The Moiré patterns were produced with double Ronchi gratings, and captured in many projecting directions.With the technology processing digital images, the experiment Moiré patterns were tracked and further analyzed with a series of analyzing techniques.This series of processing algorithms are called tunnel-exploring algorithm here.The tunnel-exploring algorithm includes tracking maximums of fringes, excavating fringe tunnels, binarizing Moiré patterns, filtering out noise, exploring fringe tunnels, extracting the track of tunnel extension, and so on.First, each of Moiré fringes is tracked based on its column pixels′ maximums.According to the maximums′ distributions, the fringes are excavated into tunnels.Each trenched width, viz.the width of pixels, is adjusted to make the tunnel link up, but not to interfere the adjacent fringes.Second, the Moiré patterns with excavated tunnels are binarized and filtered.The fringe tunnels are smoothed out by filtering out the noise on both sides of each tunnel.Last, the fringe tunnels are explored based on the distributions of both sides of each tunnel, and the track of each tunnel extension are extracted out, then the fringes′ deviations are obtained.Therefore, by tunnel-exploring algorithm processing, the fringes′ deviations were obtained.Then, they are used to reconstruct a section temperature distribution of the flow field using nonlinear auto-adjusting iterative reconstruction technique.As the result, the highest temperature reconstructed is 492℃.The rated surface temperature of the heater is about 500℃.The reconstructed section is just above the heater, so the reconstruction is considered reasonable.