The calibration of triaxial induction logging tools is commonly performed in large water tanks, which are costly and complicated to use. In contrast, calibration with a metal loop is relatively economical and convenient. A tilted metal loop is introduced to calibrate all the components of a triaxial induction tool simultaneously. We have evaluated and optimized parameters such as radius, resistance, azimuthal angle, and position of the calibration loop with the 3D finite-element method. For validation, the accuracy of the simulation method is verified with analytical solutions with consideration of the metal mandrel effect. A quantitative agreement is found between the simulation results and the measurements of a realistic triaxial induction tool with a metal mandrel. Numerical simulation results demonstrate that the presence of the metal mandrel causes the nine components of the tool to change nonlinearly with the formation conductivities in the double logarithmic coordinate. This nonlinear effect can be reduced by eliminating the background signals from the metal mandrel. After the optimization of the parameters of the calibration loop, the responses of the triaxial induction tool can be calibrated accurately.