An approach is provided for a multi-component seismic data processing that separates P-type and S-type seismic waves in an affine coordinate system. A method for separating and composing seismic waves comprises: determining base vectors of the seismic waves; transforming and separating the seismic wave in an affine coordinate system; and obtaining a signal with true amplitudes and eliminating a mode leakage phenomenon. Therefore, the method achieves the wave separation and recovers the amplitudes of separated waves simultaneously, which reduces noises to provide more precisely seismic data and to satisfy the requirement of seismic data analysis and processing.