A catalyst having high activity independent of the hydrogen concentration and low gel productivity in the polymerization of ethylene has been prepared. The preparation comprises the steps of reacting: a support comprising a magnesium halide compound having the formula (1): (RO)2−nMgXn  (1)  wherein R is a C1-C20 alkyl or a C7-C26 aralkyl, each the same or different, X is a halogen, and n is an integer 1 or 2; a compound having the formula (2): R1n1Mm1X1(3m1−n1)  (2)  wherein M is B or Al, each same or different R1 is a C1-C10 alkyl, each same or different X1 is a halogen, m1 is 1 or 2, n1 is 1 or 2 when m1 is 1 and n1 is an integer from 1 to 5 when m1 is 2; a magnesium composition containing magnesium bonded to a hydrocarbyl and magnesium bonded to a hydrocarbyl oxide, said magnesium composition having the empirical formula (3): R2n2(R3O)2−n2Mg  (3)  wherein each same or different R2 is a C1-C20 alkyl each same or different R3 is a C1-C20 alkyl, n2 is between 0.01 and 1.99, which is the contact product of a dialkyl magnesium and an alcohol in a molar ratio of alcohol to dialkyl magnesium of 1.8-1.98 mol/mol, and; a titanium halide compound having the formula (4): (R4O)n3TiX24−n3  (4)  wherein each same or different R4 is a C1-C20 alkyl, each same or different X2 is a halogen, and n3 is 0 or an integer 1-3.