The present invention relates to a passive wavelength division multiplexing device for automatic wavelength locking and a system thereof including an optical multiplexer, an optical filter, an integrated optical receiver monitor, and a tunable optical transmitter. Through wavelength locking that adjusts a wavelength of an optical signal, which changes according to an external environment such as a temperature change, into a wavelength of an optical signal having the maximum optical intensity, communication quality may be maximized by securing a stable communication channel, a locking time and a communication channel setting time may be reduced, and more robust locking may be guaranteed.