The invention discloses a process method for production of alpha-olefin by oligomerization of selective ethylene; a high-pressure reaction kettle is externally connected with a material circulation pipeline; the material circulation pipeline is provided with a heat exchanger and a gas-liquid separator; in the synthesis process of alpha-olefin, ethylene is inputted to the high-pressure reaction kettle, alpha-olefin synthesized in the presence of a catalyst and a reaction solvent is dissolved in a solvent in the kettle, and a reaction liquid containing a product flows out from the bottom of thekettle, then has heat exchanged by the heat exchanger, enters the gas-liquid separator and is subjected to gas-liquid separation; gas discharged from the top of the gas-liquid separator flows back toa gas mixing tank, and a liquid is sent back to the high-pressure reaction kettle. The invention also relates to a system implementing the process. Heat generated from the reaction is removed in time,the reaction temperature is steadily controlled, and the activity and the selectivity of the catalyst are improved.