We proposed a method to simultaneously implement quasi-phase-matching (QPM) second harmonic generation (SHG) and polarization coupling for arbitrary wavelengths in an aperiodically poled lithium niobate (APPLN). It allows for modulation of both polarization and magnitude of the SHG light by an external electric field. A method called the self-adjusting algorithm (SA) is suggested for designing the aperiodic microstructure. The numerical simulation shows that it is the competition between the SHG and polarization coupling processes, which is dominated by the external electric field, that makes the output tunable.