A novel monolithic dual-wavelength tapered laser diode based on a composite distributed Bragg reflection (DBR) grating is demonstrated. The composite DBR grating, composed of two sub-gratings with different effective refractive indices, is designed. With the aid of the lateral expansion effect of the optical field in the ridge waveguide, the dual-wavelength operation of tapered laser diode is realized by using the composite DBR grating as a narrow linewidth filter. At the ridge current of 190-300 mA and the heat sink temperature of 20℃, the tapered laser diode obtains dual-wavelength emission with wavelengths of 1025.4 nm and 1036.2 nm, respectively. The linewidths of both wavelengths are less than 36 pm, and the minimum power difference between the two wavelengths is 1.2 dB. The spectral distance between the two wavelengths can be modulated from 10.4 nm to 10.9 nm by adjusting the heat sink temperature of the tapered laser diode from 13.8℃ to 20.7℃.