The invention discloses a liquid level detecting system of liquid tanks and comprises the following components: a control chip and a monitor that are connected by a bus, wherein, a circuit of the monitor is connected with each pressure transmitter; the control chip comprises a trigger unit that is used for sending trigger commands to each unit, triggering a relay of the corresponding liquid tank that is connected with each pressure transmitter, and selecting stored liquid density, a computation unit that is used for obtaining a numerical liquid level value according to pressure parameters that are transmitted by the pressure transmitters and the selected liquid density after receiving the trigger commands; the monitor is used for displaying the numerical liquid level value and comprises asetting unit and an automatic detecting unit. The liquid level detecting system of the invention avoids manually complicated device re-debugging and re-measuring processes after liquid replacing, does not need standalone detecting devices that are respectively configured for each liquid tank when measuring the liquid levels of large number of liquid tanks, and can realize centralized detection, lower detection cost and save the detecting devices.