The invention discloses a beta-hydroxy imine titanium metal catalyst for polymerizing ethylene and a method for polymerizing ethylene. The catalyst can be prepared by the following steps: reacting an imide compound with lithium diisopropylamide; reacting the reacted imide compound with aldehyde or ketone to generate a beta-hydroxy imine ligand; and reacting the ligand with a titanium metal compound to generate the beta-hydroxy imine titanium metal catalyst. By adjusting the substituent group structure of the imide compound and the types of the aldehyde or ketone and the polymerization conditions, the controllability of the catalytic polymerization on the ethylene can be realized. The catalyst is a novel non-metallocene transition metal catalyst and has the characteristics of novel structure, high catalytic activity, easily-accessible raw materials, convenient preparation and the like.