It was studied the physicochemical properties of pre-heating treatment grain flours and in-vitro digestibility of grain starch. By analyzing the gelatinization property， swelling power， water absorption and starch composition of oat， foxtail millet and corn flours were heated by steam and baking. Results showed that: Heat treatment caused a significant decrease in the gelatinization temperature of oat flour and a significant increase of millet and corn flour(P<0.05). Heat treatment caused a significant increase in the setback of oat and millet flour and a significant decrease of corn flour (P<0.05). Heat treatment significantly decreased the peak viscosity and breakdown of corn flour(P<0.05). Different heat treatments had different trends in the effects of peak viscosity and breakdown of oat and millet flour. The swelling power of oat flour， when heated by steam and baking， decreased by 32% and 12%， respectively， and the water absorption index increased by more than 20%. But heat treatment made millet and corn flour change less. Heat treatment reduced the water solubility index of three kinds of cereal flour by 28% to 55%. The fast-digestible starch was decreased by 10% to 20%， but the slow-digestible starch was increased by 3% to 30%， and the resistant starch was increased about 20%. The oat starch composition was most affected by heat treatment. The particle diameters of oat， millet and corn starch were about 5， 10 and 15 μm respectively. After heat treatment， the starch of oat， millet and corn were agglomerated and bonded， especially oat starch. The physical and chemical properties of grain flours were affected by appropriate pre-heat treatment， then improved the processing properties. The starch composition was changed by heat treatment， reduced digestibility， and improved the functional properties.