In order to implement non-contact detection for liquid level less than 100mm in height, the method for changing planar capacitive edge electric field parameters by liquid level was adopted. The working principle of planar capacitive sensor was analyzed, and the effect of planar capacitive sensor structure parameters on sensitivity and penetration depth was studied. The method of structural optimization design on sensors was proposed. The non-contact detection system for lower liquid level was designed based on planar capacitive sensors. The measured data of pure water, detergent solution and ink within 100mm was obtained by experimental verification. The experimental results show that the system with linear output is stable. The repeatability error is about ±0.28%, and the measurement error is within 7.8% before data correction. The results are helpful for non-contact detection for lower liquid level.