The invention discloses a detection device and method of a 3.7V cell single-string protection plate. The detection device comprises a large power voltage source, an output adjustable voltage circuit, a power supply switching circuit, a simulated load, a controller and an accessory circuit thereof, a display module and a button keyboard. The controller and the accessory circuit thereof are connected with the output adjustable voltage circuit, the simulated load, the display module and the button keyboard. An input end of the button keyboard is connected with the large power voltage source and the output adjustable voltage circuit, and an output end is connected with a cell protection plate. An output end of the cell protection plate is connected with the simulated load. The controller and the accessory circuit thereof use a PIC16F1823 single-chip controller as a core. The output adjustable voltage circuit uses an LM2596 as a core. PWM pulses are input to a fifth pin of the LM2596, so that continuous adjustment of an output voltage is realized, and the range of the output voltage is 2.0-4.5V; in addition, the structure is simple, the cost is low, and the operation is simple and convenient.