A method for initial alignment of an inertial navigation apparatus, comprising the following steps: providing an apparatus loaded with a sensor, and preprocessing the sensor; carrying out relative alignment to calculate an installation error angle of the sensor; carrying out absolute alignment to calculate an installation attitude angle error of the sensor to increase an accuracy of an error attitude angle calculated during the relative alignment. The relative alignment process calculates a relative error attitude angle, the relative error attitude angle being used as the initial value for attitude error in a stat vector in the absolute alignment process, thereby accelerating convergence of the Kalman filter. Alignment precision is further enhanced by the absolute alignment process.