There are a number of bubbles when Cr12N stainless steel is smelted. But its number is smaller and smaller with the increasing of solidification pressure. When the melting pressure is 0.6 MPa and the solidification pressure increases from 1.0 to 1.6 MPa, the average number of bubbles decreases from 46.37 to 9.46 per square millimeter. Bubble number is reduced by 20.4%. The number of bubbles whose diameters are greater than 20 μm is reduced to 17.4%, while the number of bubbles whose diameters are less than 5μm increases by 37.7%. With 0.3 MPa melting pressure and 1.6 MPa solidification pressure, the average bubble size content near the lower surface is 23.9% of that near the upper surface. Average bubble size content at the edge is 25.9% of that at the center. According to the actual nitrogen content in steel ingot calculated by the established mathematical model, no bubbles of high nitrogen steel ingot may be obtained when melting pressure is 0.6 MPa and solidification pressure increases to 1.8 MPa.