We studied solar coronal X-ray jets by MHD numerical simulations with thermal conduction effects based on the magnetic reconnection model. Key physical processes are included, such as the emergence of magnetic fluxes from the convection zone, magnetic reconnection with the coronal magnetic fields, heat conduction to the chromosphere, and chromospheric evaporation. High-density evaporation jets were successfully reproduced in the simulations. The mass of the evaporation jets M is described as M = 6.8 × 1012 g(B/10 G)15/7(Tcor/106 K)5/14 × (sflare/5000 km)12/7(t/400 s), where B is the magnetic field strength, Tcor is the coronal temperature, sflare is the loop height, and t is the duration of the ejection.