Waveguide optical coding device for optical ADC belongs to the optical technical field and relates to the optical signal treatment and integrated optical device. The device is composed of 2<N>-1 longitudinal waveguides and N horizontal waveguides integrated by one chip, the longitudinal waveguides and the horizontal waveguides are connected by waveguide connecting structural units A, B or C, or connected in a right-angled intersection manner or not connected. The invention is substantially based on an optical total internal reflection principle and designs different waveguide connecting structural units for realizing optical transmission and optical power budget, and the spatial positions of the waveguide connecting structural units on the coder correspond to the binary coding thereof so as to accomplish the coding process in ADC. The waveguide optical coding device for optical ADC provided in the invention has the advantages that the coding speed is quick, the performance is stable and reliable, the design is simple, the manufacturing difficulty is low, the cost is low, the volume is small and the like; and the coder and the waveguide array grating can be integrated. Thus, the invention is in favor of improving the stability and reliability of the system and reducing the cost.