The present invention discloses a multi-turn absolute value encoder, comprising: a detection module, a power supply working module and a power-off working module; the detection module is used for performing power-on detection and power-off detection; when the power-on is detected, the power supply working module works; when the power-off is detected, the power-off working module works; the power working module includes a single-turn absolute value encoder and a single-chip microcomputer, the single-chip microcomputer collects rotor position information of a motor via the single-turn absolute encoder; the power-off working module includes a common encoder and a low-power single-chip microcomputer, and the low-power microcomputer collects the rotor position information of the motor through the common encoder. The multi-turn absolute value encoder with low-cost high-performance design combines advanced algorithms, to achieve low cost, high precision, small size and unlimited measurement range is unlimited, and achieves continuous long-term use without external power supply. The invention also discloses a working method of a multi-turn absolute value encoder.