The invention discloses a preparation method of a polyolefins hot melt adhesive and the prepared polyolefins hot melt adhesive. The preparation method comprises: performing a heating reaction on polyolefin, an antioxidant, polyethylene wax and hydrogenated petroleum resin to obtain the polyolefins hot melt adhesive, wherein a preparation step of the hydrogenated petroleum resin comprise: performing a hydrogenation reaction on C5 petroleum resin and a hydrogenation catalyst containing Pt, a ZSM-5 molecular sieve and a ZSM-12 molecular sieve by adopting a hydrogenation catalyst under the conditions that the temperature is 250 to 300 DEG C, the pressure is 5Mpa to 7Mpa, the liquid hour space velocity is 1h<-1> to 3h<-1> and the hydrogenation/petroleum ratio is (500 to 800): 1, so as to obtain the hydrogenated petroleum resin. The hot melt adhesive disclosed by the invention has good viscosity and small odor.