The invention provides an inflow port structure for a biological retention facility, which comprises a top cover, an overflow grille and a barrel of which the top is open. The overflow grille is arranged along the circumferential direction of the top end of the barrel; the top end of the barrel is in parallel and level to the side edge of a road; an inflow port is formed at one side of the overflow grille, which is close to the road; a filtering device is arranged inwards at the position of an opening of the barrel; the side wall of the barrel is connected with a water outlet pipe; and a wateroutlet of the water outlet pipe is lower than the plane where the top end of the barrel is positioned. According to the inflow port structure for the biological retention facility, which is providedby the invention, by arranging the filtering device and the overflow grille, in a case of light rain, after sundries in rainfall runoff are filtered by the filtering device, when the sundries are accumulated to a certain amount, the sundries directly flow into the biological retention facility through the water outlet of the water outlet pipe; and in a case of heavy rain, the sundries directly overflow into the biological retention facility through the overflow grille, so as to implement low-flow water outlet pipe inflow and high-flow overflow dispersed inflow modes, reduce scouring on plantsnear an inflow port and ensure excellent operation of the biological retention facility.