The invention relates to a device and method for onsite calibration of a metering instrument. The device comprises a calibrating medium acquisition device and pipeline assembly, a standard meter and pipeline assembly, and a device and pipeline assembly connected in series in sequence, the device and pipeline assembly is detachably connected with a to-be-calibrated metering instrument, the standardmeter and pipeline assembly comprises a plurality of standard meter connection pipelines connected in parallel, the total lengths of meter front straight tube sections, standard meters and meter rearstraight tube sections of different standard meter connection pipelines are the same, the device and pipeline assembly detachably connected with the to-be-calibrated metering instrument comprises a to-be-calibrated metering instrument front valve, a to-be-calibrated metering instrument rear valve, an upstream connecting pipe and a downstream connecting pipe, and one ends, far from the to-be-calibrated metering instrument, of the upstream connecting pipe and the downstream connecting pipe are respectively connected with the to-be-calibrated metering instrument front valve and the to-be-calibrated metering instrument rear valve through rapid connecting devices. The device can be used for indoor calibration and onsite calibration.