Abstract: By using the natural laminar airfoil RAE5243 as the research object, the TSP(Temperature Sensitive Paint) transition detection technique is studied in the 0.6m transonic and hypersonic wind tunnel in China Aerodynamics Research and Development Center. The transition detection tests of the model's baseline configuration with and without the shock control bump are conducted at Mach number 0.73 and 0.75, respectively. Focusing on the lack of quantitative analysis method, an automatic location algorithm based on the temperature gradient is proposed, which includes the image preprocessing, the transition point positioning and filtration, and the transition location's calculation. The model's temperature distribution and transition location under different test conditions are compared, and the deviations between repeatable transition detection tests' results are very small, which ensure the reliability of the technique. The transition location of the baseline configuration with the shock control bump is behind that of the baseline configuration at the same Mach number. The same model's transition location at Mach number 0.75 is behind that of 0.73. The TSP result and CFD result match well and the tendency is the same.