Abstract: The inner flow in a 45°sharp-edged T-junction is measured on the pressure loss of the exhaust system. Pressure loss of compressible combining flow at two junctions is obtained at different flow conditions. Junctions are manufactured with area ratios of φ=1 and 1.56 respectively. In addition, the axes in all branches are coplanar and the corners at the point of intersections between lateral branch and main branch are sharp edged. Comparative analysis the data of pressure loss, the results indicate that pressure loss is mainly dependent of "junction loss" in the junction flow. The static pressure in the common branch is always lower than that of the inflow across the entire range of the mass flow rate ratio. Additionally, with increasing M₃, the compressibility of the fluid significantly increases. The static pressure in the inflow branches 1 and 2 are equal in the present study. Flow parameters have been related to the Mach number in common branch and the mass flow rate ratio between branch and duct. As the mass flow rate ratio of branch and duct increased, the total pressure loss coefficient K₁₃ and K₂₃ increased first and then decreased, while the peaks are different. The variation in the total pressure loss coefficient with Mach number in common branch is fairly small in the range of 0.13 to 0.31. However, along with the Mach number M₃ increases to 0.59, the coefficient increases more rapidly. The results provide reference for the research of pressure loss and the boundary condition in one-dimensional junction compressible models.