A self-calibrating fiber-optic level sensor system composed of a fiber-optic pressure sensor and two optical fiber level probes is described. The pressure sensor is based on the photoelastic effect and compensated with a method of optical bridge. The optic fiber probe is based on an optical intensity modulation method in which the reflected optical power by the probe sensitively depends on the refractive index of the surrounding medium. In the self-calibrating system two optical fiber probes are set at two heights of the oil tank, which are as two basic reference points The pressure sensor is connected to the bottom of the tank to measure the static pressure continuously. As the liquid level passing the reference point the probe gives out a signal to the computer to correct the measurement errors and recalibrate the sensor. The system has been applied to actual measurement in industry and the long term accuracy has reached to 0.2$% of full-scale.