A side-coupled optical-fiber liquid level sensor is proposed to realize intrinsically safe measurement to liquid level in flammable environments. The sensor consists of two parallel side-polished fibers is based on the different coupling coefficient between the fibers in different media according to the Fresnel equation. One of the fibers is for emitting and the other is for receiving, and a reflector is attached to the end of the fibers to enhance the power of light. The power of the light from the top of receiving fiber is measured by the signal processing circuit which is mainly organized by an instrumentation amplifier and a correlator. This sensor is fabricated in the laboratory and the results of the experiments show good performance. It is demonstrated that the sensor is safe and sensitive, but there is still a lot of work to do before its commercial usage.