The invention discloses a small GM counting tube wide-range monitoring instrument. The instrument comprises a high-voltage module used for providing high work voltage for a GM counting tube, the GM counting tube used for monitoring the dose rate level of an environment in real time, AD integral collecting units used for collecting integrals of output signals of the GM counter tube, a high-voltagemeasuring unit used for measuring the output voltage of the high-voltage module, a shaping and pulse counting unit used for monitoring the pulse count number of the output signals of the GM counter tube in real time, and an MCU circuit used for logically judging data of each collecting unit and judging whether the pulse count number of the GM counter tube or a collecting result of the integrals ofthe output signals of the GM counter tube is adopted for measuring a dose rate. On the basis of the calculation of a judgement result, a final dose rate measuring result is obtained; the technical effect of automatic switching between a low dose rate level and a high dose rate level of the output signals of the GM counter tube is achieved.