In this paper, the 5wt. % ZrB2p /6061Al composite was prepared by in-situ synthesis and the microstructure of laser welding and mechanical properties were studied. XRD and EDS analysis show that 5wt. % ZrB2p/6061Al composites were successfully prepared through the Al-K2ZrF6-KBF4 in-situ reaction system. Through OM and SEM analysis, compared with the matrix 6061Al alloy, the heterogeneous nucleation effect and pinning effect of the nano ZrB2 particles has a certain grain refinement effect on the matrix grains of the composite, but the existence of nanoparticle clusters makes the refinement effect limited. During laser welding, under the condition of complete penetration, a high-power and high-speed welding of 3.6 kW and 40 mm/s can be ultilized to obtain a well-formed weld. The rapid laser melting process and solidification made the matrix grains further refined, a large number of ZrB2 clusters basically disappear, and ZrB2 particles were basically evenly dispersed. By analying the migration behavior of ZrB2 particles, it is found that the melt agitation and rapid solidification process of the laser molten pool achieved the twice distribution of ZrB2 particles. The optimization of the weld microstructure improves the Vickers hardness and the tensile strength of the welded joint, respectively up to 57.3 HV and 125.17 MPa. And the strengthening mechanism of weld is discussed.