Abstract: 6 mm thick hot rolled 7a52 aluminum alloy was welded by using fiber laser. The microstructures and properties of welded joints were studied at the same welding heat input with different welding parameters and different welding heat input. The result shows that the microstructure of welded joint consists of larger grain with equiaxed grain in the form of “snow” shape, the grain size was increased with the increase of welding heat input. With the increase of welding heat input, the loss of Mg element and Zn element were increased gradually. At the same welding heat input, high welding speed and high welding power can relatively reduce the burning loss of Mg and Zn elements. The results of hardness test showed that the microhardness of base metal is about 110 HV and microhardness in fusion center zone is the lowest, and microhardness curve in the form of “U” shape from weld center to the parent metal. With the increase of welding heat input, the joint can obviously improve the impact toughness and tensile strength. At the same welding input, the joint at high welding speed and high welding power input has lower impact toughness and higher tensile strength , the maximum tensile strength is 341.05 MPa , accounts for about 69.8% of the base metal. The tensile fractured surface of laser welded 7A52 aluminum alloy is plastic and brittle mixed fracture.