Based on magnetic effect characteristics of coal gas emission, by establishing experimental system of the gas emission magnetic effect, the emission process of unmagnetized and magnetized coal sample gas is tested and the influence of constant magnetic field on the coal sample emission gas is studied. The initial experimental data shows that the smaller initial emission rate of gas is (the value of f is large), the smaller coal simple gas emission will be; otherwise, the larger initial emission rate of gas is(the value of f is small), the larger coal simple gas emission will be. Both of them are affected by magneted time. When the magnetic field is removed, Δ p does not restore to the original value immediately and maintains a certain amount of time. The preliminary study on its mechanism shows that the b value of the samples with large f values decreases after magnetization. With the voltage increases, the surface lowering values of magneted samples are lower than those of unmagneted ones. Namely under the action of magnetization, the reduce of gas adsorption space reduces the adsorption quantity, and the instantaneous gas pressure gradient decreases, so as to slow the gas radiation initial speed. However, small f value has opposite results.