Thermal barrier coatings (TBCs) were made on the round bar substrates of which radii were 5, 10 and 15mm. In addition to the round bar substrates, the TBC was made on a plate substrate. First, NiCoCrAlY was pressureless plasma-sprayed as bond coating, and then zirconia with 8 mol% yittria was air plasma-sprayed as top coating. The TBC specimens were exposed in air atmosphere at 1373K for 0h, 200h or 500h. The radial strain was first measured with the strain scanning method using high energy synchrotron X-rays. The hoop and axial stresses of the round bar specimens were measured using laboratory X-rays with successive removal of the surface by polishing. Using these measured stresses and strain, the distributions of the 3-dimentional components of the residual stress in the top coating were determined. The spalling stress became a maximum at about 50μm apart from the interface. This position corresponded to the location of initiation of the spalling cracks. The maximum of the measured spalling stress increased with the decrese in the radius of curvature. The difference of the measured distribution of the residual stress from the calculated distribution of the thermal residual stress was explained on the basis of the characteristic of the top coatings, such as the stress relaxation due to sliding between lamelli, a binding effect by the interface roughness and the spalling stress induced by the interface roughness.