The invention discloses a bio-control type liquid medicine fertilizer synergist and a using method thereof. The synergist comprises the following components in percentage by weight: 25-30% of a sugar-based surfactant, 8-10% of a polyoxyethylene ether surfactant, 5-7% of a bio-control bacteria agent, 6-8% of a biostimulant, 1-4% of a stabilizer and the balance of water. The using method comprises the following steps: S1, diluting the bio-control type liquid medicine fertilizer synergist by 3000-5000 times to be added into a medical fertilizer solution; S2, uniformly spraying the medical fertilizer solution on the positive and reverse sides of leaves; S3, thinning spray droplets, and controlling the flow to be 0.3-0.5L/min; increasing the sprayed medicine and fertilizer approaching speed, controlling the speed to be 2-2.5m/s, and forming a water film coating the whole leaf on the positive and reverse sides of the leaf. The bio-control type liquid medicine fertilizer synergist disclosed by the invention effectively solves the problems such as low medicine and fertilizer utilization rate, high cost, environmental pollution and the like and has the bio-control and regulation functions.