73 eases of malignant tumour were cured by an adjustable three folded CW sealed-off CO2 laser with a power density of 105-333 W/cm2 at the "knife head". The 2-year survival is 76.7 %. Clinical practice shows that laser evaporation of malignant tumour do not results in sputter ing and proliferation of cancer cells, and it is also effective for the later period hopeless cases, so it has advantages in comparison with conventional treatment methods.