Abstract: At present, the static calculation of downhole tool attitude angle relies heavily on triaxial sensors. However, system errors in the measurement process may lead to inherent distortion, so it is necessary to fully compensate the system errors in order to get accurate attitude angle information. Based on the attitude error propagation model, it is proposed to divide the output trajectory of the triaxial sensor at different attitudes into different regions, and approximate the correction matrix at different attitudes by fusing piecewise polynomial and spline interpolation, so as to fully compensate the system errors. Finally, the precision of the method proposed above is verified by high-precision calibration experimental device. When the well inclination angle is 3.006°, (mean±standard deviation) of the attitude angle error are calculated, among which the error of azimuth angle, well inclination, and tool face angle is 0.010 9°±0.079 4°, 0.001 2°±0.002 1°, and is 0.005 7°±0.039 9°, respectively. The verification test results of attitude angle error statistics show that the proposed method is characterized by good compensation effect on attitude angle errors, which can effectively solve non-linear problems in the attitude calculation process, thus improving the overall precision of downhole tool attitudes.