The invention discloses a voltage monitoring method, state estimating method and detecting device for a liquid metal battery. The voltage monitoring method for the liquid metal battery comprises the following steps: selecting L groups of first adjacent liquid metal battery packs from N liquid metal batteries which are connected in series, and acquiring the terminal voltages of the L groups of thefirst adjacent liquid metal battery packs; selecting K groups of second adjacent liquid metal battery packs from the N liquid metal batteries which are connected in series, and acquiring terminal voltages of the K groups of the second adjacent liquid metal battery packs; expressing the terminal voltages of the L groups of the first adjacent liquid metal battery packs and the terminal voltages of the K groups of the second adjacent liquid metal battery packs as the sum of each liquid metal battery voltage to form an initial voltage equation set; performing redundancy eliminating processing on the initial voltage equation set to obtain a voltage equation set with full rank coefficients; calculating to obtain the voltage of each liquid metal battery according to the voltage equation with thefull rank coefficients. According to the method, the voltage measurement error of a liquid metal battery monomer with a low voltage and a wide platform can be effectively reduced, and the state estimating precision can be improved.