  We present the calibration of the Insight-Hard X-ray Modulation Telescope
(Insight-HXMT) X-ray satellite, which can be used to perform timing and
spectral studies of bright X-ray sources. Insight-HXMT carries three main
payloads onboard: the High Energy X-ray telescope (HE), the Medium Energy X-ray
telescope (ME) and the Low Energy X-ray telescope (LE). In orbit, the
radioactive sources, activated lines, the fluorescence lines and celestial
sources are used to calibrate the energy scale and energy resolution of the
payloads. The Crab nebular is adopted as the primary effective area calibrator
and empirical functions are constructed to modify the simulated effective areas
of the three payloads respectively. The systematic errors of HE, compared to
the model of the Crab nebular, are less than 2% in 28--120 keV and 2%--10%
above 120 keV. The systematic errors of ME are less than 1.5% in 10--35 keV.
The systematic errors of LE are less than 1% in 1--7 keV except the Si K--edge
(1.839 keV, up to 1.5%) and less than 2% in 7--10 keV.
