Aiming at the problem that the formaldehyde damages human health in daily life, an optical sensor capable of detecting the concentration of formaldehyde solution rapidly and accurately in real time is designed by using the rigorous coupled wave analysis (RCWA) method. The sensor uses the porous zirconia (ZrO2) mesoporous material as the bearing unit of formaldehyde,and the titanium dioxide (TiO2) and silicon dioxide (SiO2) gratingsact as a layered composite structure composed of a waveguide layer and an optical coupling layer respectively.The transmission spectrum of the sensor is calculated by RCWA method. The relationship model between the wavelength of the transmission resonance peak and the concentration of the formaldehyde solution to be measured is established and its sensing characteristics are analyzed. The results show that the sensor has high sensitivity and good repeatablestability, the quality factor Q is 1 261, the sensitivity is up to 0.101 nm/%, and the realtime dynamic monitoring of the concentration of formaldehyde solution can be realized.