In order to accurately measure the dispersion of quasi-transverse wave(TE) and quasi-transverse magnetic wave(TM) in meter-level linear slit waveguides, a dispersion-measuring optical path of Mach-Zehnder interferometer(MZI) is designed. The measurement principle of phase fitting method and balanced wavelength method is introduced, and the measurement is carried out in combination with the measurement optical path. The measurement results show that the accuracy of dispersion measurement can be further improved by removing the crosstalk noise between polarization modes. The dispersion of the waveguide can be effectively controlled by adjusting the slot size. When the slot thickness is 0.1 μm, the waveguide has near zero and flat dispersion in the wavelength range of 1 440~1 640 nm.