The microstructures and mechanical properties of a new type of piston type B aluminum alloy and ZL109 were compared. The results show that the composition of Al, Si, Al6Mn and Al5FeNi of ZL109 is composed of Al, Si, Al6Mn, Al2Cu, Al1.9CuMg4.1Si3.3 (Q phase), AlNiCu and more Al5FeNi. The α-iron phase in the B-type aluminum alloy showed fish bones and lumps, which reduce the cleavage of the needle-like β-iron in the ZL109 tissue. The AlNiCu phase of La and Ce elements can block the grain boundary, and the role of matrix deformation, and the organization also produce Al2Cu, Al5FeNi and Al1.9CuMg4.1Si3.3 enhanced phase; therefore, B-type aluminum alloy mechanical properties is better than ZL109, and by the piston bore size specifications is less affected. The fracture type of B type aluminum alloy is quasi-cleavage fracture, showing dimple, tongue pattern and tearing edge.