This paper focused on the key technologies of microfiber production by direct spinning, discussed the relations between fiber´ s linear density and factors including material´ s relative molecular weight, nozzle´ s size, annealer and blowing set, spinning path length, spinning speed, etc. Finally, the authors concluded that all the factors which could improve melt flow behavior or reduce filament´ s drawing stress were conductive to reduce fiber´ s linear density.