In order to improve the density of metal parts fabricated via selective laser melting（SLM）,the characteristics of the single-track molten pool were investigated,and the influences of scan speed and laser power on the pool width were discussed,with a direct relation between the width of powder-free region around the molten pool and the molten pool width being summarized.Then,the joint defaults of scan lines during continuous scanning were analyzed.Moreover,according to the forming characteristics of the single-track molten pool,a layer stagger strategy of laser scanning was proposed.Experimental results indicate that,by taking the proposed strategy,the density of metal parts increases to about 100%,the molten pools between inner layers and inter-layers are jointed compactly,and the tensile strength,elongation and micro-Vickers hardness of the parts reach 636MPa,15%~20% and 250~285,respectively.It is thus concluded that the proposed layer stagger strategy greatly improves the density and mechanical performance of metal parts fabricated via SLM.