The invention discloses an over-limit alarm circuit for oil level of lubricating oil of a fuel oil generator. The over-limit alarm circuit comprises a liquid level sensor used for detecting the oil level of lubricating oil, an operational amplifier A1, an operational amplifier A2 as well as a low-voltage source Vmin and a high-voltage source Vmax which are corresponding to high and low limit set values of the oil level of the lubricating oil, wherein a reversed-phase input end of the operational amplifier A1 and a same-phase input end of the operational amplifier A2 input a voltage value corresponding to an output value of the liquid level sensor; a same-phase input end of the operational amplifier A1 inputs the low-voltage source Vmin; a reversed-phase input end of the operational amplifier A2 inputs the high-voltage source Vmax; and a switching signal output by the operational amplifier A1 and the operational amplifier A2 controls an alarm device to emit an alarm signal or not by an electronic switch. The over-limit alarm circuit has the characteristics of low manufacturing cost, high monitoring precision, reliable work and the like, and can be used for carrying out real-time monitoring and over-limit alarming on the oil level of the lubricating oil.