The invention discloses a distribution transformer transformation ratio measuring instrument and a distribution transformer transformation ratio calculation method. The distribution transformer transformation ratio measuring instrument comprises a primary measurement module for measuring voltage and current on the high voltage side of a distribution transformer, a secondary measurement module for measuring voltage and current on the low voltage side of the distribution transformer, and a control instrument for controlling the primary measurement module and the secondary measurement module. Each of the primary measurement module and the secondary measurement module comprises a voltage signal acquisition device for acquiring voltage signals, a current signal acquisition device for acquiring current signals, a communication module for communicating with the control instrument, and a processing module for controlling the voltage signal acquisition device, the current signal acquisition device and the communication module. Compared with the prior art, through the distribution transformer transformation ratio measuring instrument provided by the invention, the transformation ratio of the distribution transformer can be measured in real time conveniently, so that reference is provided for regulation and control of the distribution transformer and trouble removal of the distribution transformer.