Abstract：The tensile strength can be determined from the split test of a disk specimen，or Brazil test. However，yield and fracture will occur in the rock near the loading points under high stresses，which is different from its testing principle. Two flats are induced to the Brazilian disk as loading sufaces for improving the stress states. The flats have the uniform deformation，but not the uniform stress，under the compression of testing machine. The modification coefficients for calibrating the tensile strength and Young¢s modulus are calculated based on the results of finite element analysis. In a given force compressed on the flats，the tensile stress in the center of disk decreases with the central angle of flats，and the ratio of compressive stress to tensile stress increases as well. So it is better to choose the smaller central angle for getting the true tensile strength. On the other hand，it is better to choose the greater central angle for the convenience of the flat milling and the facilitation of compression. So 30°is suggested for the available central angle of the flats. It is difficult to determine the fracture toughness KIc of rock from the Brazilian test with the flattened disk specimen，for the disk does not crack along the symmetric line and the loading method of testing machine is controlled by compression deformation.
