An optical waveguide interference chip with a multi-layer planar structure was designed, and the integrated chip was fabricated successfully after its structure and the material parameters were optimized using the mode theory of optical waveguide. Far-field interference fringes with a high contrast are achieved by the dual-guide waveguide structure inside the chip. Within an experimental error, experiments demonstrate that the interference fringe pattern generated from the integrated chip can be explained and predicted by Young′s double-slit theory, and the fringe moves under a minor environment change. For humidity and alcohol gas, the detection sensitivity of the chip can reach about 100 ppm level with enough temperature stability during estimate test, which demonstrates its potential applications in sensing environment gas with low concentration and provides a new platform to develop an integrated gas sensor with high sensitivity.