The invention discloses an oil injection device for a circuit board and an application method thereof. The oil injection device comprises two automatic mechanical oil injection cabinets, a turnover mechanism and sliding rails. The sliding rails includes a first sliding rail, a second sliding rail and a turnover sliding rail, wherein the first sliding rail and the second rail are arranged inside the two automatic mechanical oil injection cabinets, and the overturn sliding rail is separated from the first sliding rail and the second sliding rail. A turnover clamping device for fixing the circuit board is arranged on the turnover sliding rail. A scanner, a programmable main control computer, a spray head, a spray head rail and an oil barrel matched with the spray head are arranged inside each automatic mechanical cabinet. According to the oil injection device for the circuit board, the programmable master control computer controls the spray head to operate so that the oil can be sprayed on the circuit board according to the printing track flexibly and freely, therefore, oil is not wasted, production cost is reduced, and environment is not polluted. A turnover master control computer is used for controlling a turnover motor, the turnover motor drives the turnover sliding rail to turn over by 180 degrees, therefore, the circuit board can be turned over automatically, production efficiency is improved, and the health of operators is prevented from being harmed.