Taking magnetic prospecting in the Jurassic coalfield of northern Shaanxias an example, this paper describes techniques and geological effects of magne-tic prospecting in the fire area. The Jurassic coalfield in northern Shaanxi ischaracterized by gently-dipping strata, and has a great abundance of sideriteand pyrite nudules in the overlying rocks. The burnt rock formed by sponta-neous ignition of the coal hed has relatively strong magnetism, whose measuredcurves are complex in shape and show indistinct regularity. Through a compa-rison and analysis of △T anomaly curves along the profile of known outcropsand the exploration peofile, combined with diagnostic points of magnetic mea-surement curves, the present paper delimits the boundary of fire area of thecoalbed. Drilling demonstrates that the boundary of fire area inferred by thismethod has rather high precision and satisfactory geological effects.