The invention relates to a synthesis method of poly alpha-olefin. The synthesis method comprises the following steps: carrying out reaction on a C8-C12 olefin monomer for a certain time under the action of a Ziegler-Natta catalyst system; after the reaction is finished, adding a quenching agent, finishing reaction and stopping stirring, extracting heat by virtue of external circulation, lowering a system temperature to room temperature, then adding an initiating agent, introducing BF3, controlling a polymerization temperature, reacting for 0.5-3 hours, and then carrying out aftertreatment, so that a poly alpha-olefin oligomerization mixture is obtained.