The fluidity of molten pool is analyzed with CO2 laser welding on Al-ZL101/TiB2-Al triple plates. Scan electron microscope (SEM) and hardness tester are used to observe the TiB2 distribution and measure the hardness. The fluidity of molten pool is inferred according to the TiB2 distribution and hardness values of weld seam. In the incomplete penetration, a convection loop is presented and the strongest convection locates at the neck of keyhole where the highest hardness and TiB2 volume fraction are presented. In the full penetration, two convection loops are presented on the top and bottom surfaces of molten pool, respectively. The convection is stronger at the bottom than that on the top so that it has higher TiB2 volume fraction and hardness. The slightest convection occurs in the link of two loops, i.e. the center of weld seam where the highest hardness and TiB2 volume fraction are presented because of the smallest reduction of TiB2 flowing away with the convection.