The invention discloses a low-field nuclear magnetic resonance-based detection method of fat content for living animals. The method comprises the following steps: separately collecting nuclear magnetic resonance signals of lean meat and water in a living animal to be measured by using an IR sequence, bringing the nuclear magnetic resonance signal of lean meat in the living animal to be measured in a working curve 1 of chicken, and calculating mass of the lean meat; bringing the nuclear magnetic resonance signal of water in the living animal to be measured in a working curve 1 of water, and calculating mass of water; collecting a resultant magnetic signal of the living animal to be measured by using a CPMG sequence; bring the obtained mass of lean meat and the obtained mass of water in a working curve 2 of chicken and a working curve 2 of water respectively, in order to obtain CPMG sequence nuclear magnetic resonance signals corresponding to lean meat and water, subtracting the CPMG sequence nuclear magnetic resonance signals corresponding to lean meat and water from the resultant magnetic signal of the living animal to be measured, and bringing the value in a working curve of edible oil, in order to obtain the mass of fat. The method has the advantages of non-destructive rapid determination of fat content for living animals without pretreatment process, and low usage cost.