The contrast experiments between 8 lightweight aggregate concrete entity beams and 4 common concrete entity beams are compared and failure modes are studied. The research indicates that the cracking moment for lightweight aggregate concrete of the same strength grade are slight larger than ordinary concrete beams . Aggregate categories have a little influence on the cracking moment. The cracking moment increases with the strength grade improving of lightweight aggregate concrete. The cracking moment of fly ash pottery particle of the wet in advance have a disadvantageous influence on the specimen cracking moment.