Abstract: The atomization characteristics of a new type air assisted atomizer have been investigated for heavy oil with Engler viscosity more than 20,and compared with "Y" type atomizer commonly used in industry.A standard diffraction based sizing system (i.e.Malvern) is applied to this investigation .The results reveal the influences of the air pressure,fuel pressure,and air/fuel ratio on the atomization characteristics,the influence of the fuel pressure on the spray angle,and demonstate the fuel atomization superiority of this new-type atomizer over the "Y" type atomizer in atomization.