In order to take advantage of the ease of demodulation of the intensity-modulated fiber-optic sensor, an intensity-modulated liquid level sensor is proposed. The sensor consists of three no-core optical fibers. Among them, the no-core fiber 1 and no-core fiber 2 are cascaded to form a measuring arm, and no-core fiber 3 constitutes a reference arm. The simulation analysis show that if the length of no-core fiber is shortened by 1 mm, the transmission peak wavelength is increased by 25.46 nm. In the 0~50 mm liquid level range, the measured sensitivities of the sensor in the liquid environments, namely water, 5% NaCl, 10% NaCl and 15% NaCl aqueous solutions, are 0.069 5 dB/mm, 0.074 73 dB/mm, 0.077 49 dB/mm and 0.082 71 dB/mm, respectively. The linearities of the sensor are 0.998 25, 0.998 49, 0.988 11 and 0.995 13, respectively. The proposed sensor can eliminate the influence of optical power fluctuation and ambient temperature variation with good repetition, and maybe has a potential application in the petrochemical industry.