Through the waveguide structure design and dispersion engineering, based on the soliton pulse compression, self-phase modulation, and optical wave breaking, a 0.22 m anomalous dispersion tantalum pentoxide waveguide cascaded with a 0.9 m normal dispersion tantalum pentoxide waveguide was used to produce a flat optical frequency comb with a 4 dB flatness and 60 nm bandwidth in the 1 520 nm to 1 580 nm. The spectrogram evolution during the pulse transmission process was analyzed through the X-Frog technique, and the coherence of the optical frequency comb were also studied. The analysis indicates that the self-phase modulation and optical wave breaking effects make the comb spectrum envelop broadened and flattened. The first-order mutual coherence function calculation indicates that the optical frequency comb has good spectral coherence. The simulation results show that the tantalum pentoxide integrated nonlinear optical waveguide has a good prospect in the generation of high repetition rate flat coherent broadband optical frequency comb.