We have experimentally offset-locked the frequencies of two lasers using electromagnetically induced transparency(EIT)spectroscopy of 85Rb vapor with a buffer gas in a magnetic field at room temperature.The magnetic field is gen-erated by a permanent magnet mounted on a translation stage and its field magnitude can be varied by adjusting the dis-tance between the magnet and Rb cell,which maps the laser locking frequency to the space position of the magnet.This frequency-space mapping technique provides an unambiguous daily laser frequency detuning operation with high accuracy.A repeatability of less than 0.5 MHz is achieved with the locking frequency detuned up to 184 MHz when the magnetic field varies from 0 up to 80 G.