Using CO2 laser, Laser Lap Welding for dissimilar metals of 5A05 aluminum alloy (upper side) and ST04Z galvanized steel sheet (lower side) that both of 1mm thickness was experimented. Moreover, the microscopic structure, mechanical performance of weld joints were also analyzed and tested. The experimental results indicated that: typical melt-brazed lap joints were fused by melted 5A05 and un-melted ST04Z sheet. Fractures basically occurred in heat-affected zone (HAZ) of 5A05. Its density was 94MPa, acknowledged as gliding fracture.