A method and device for controlling a wavelength of a light emitting assembly. The device comprises a microcontroller, a light emitting assembly temperature control unit, an analog-to-digital converter, a digital-to-analog converter, a storage unit, a thermistor of a negative temperature coefficient in a TOSA component, and a TEC assembly. The microcontroller comprises an ADC input interface, a DAC output interface, a GPIO output interface, an external communication interface, and a memory interface. The light emitting assembly temperature control unit comprises a turn-off enable control circuit, a temperature detecting circuit, an error amplification-comparison-compensation unit, a TEC voltage/current limitation circuit, a TEC voltage/current detecting circuit, and a TEC differential voltage driver. The method and device are simple and flexible, implements a precise control of the wavelength, and also considers an adjustment function of the wavelength.