A new technique capable of on-line generating SO(2)+CO(2)+N(2) shielding gas via thermal chemical reaction between compressed air and a mixture of C and S powder was introduced in the present study. The test results in both laboratory and foundry indicate that the on-line generated gas is able to provide effective protection to Mg melting bath up to 730 degrees C as SF(6)+N(2) shielding gas does, while its running cost is 30% less than of the latter.