The invention relates to a daytime tunnel portal section lighting standard calculating method based on safety visual cognition. The daytime tunnel portal lighting standard calculating method comprises the following steps: (a) setting light environment parameters inside a tunnel portal section; (b) confirming a characteristic position inside a tunnel, and measuring the average pavement brightness L of the characteristic position inside the tunnel; (c) placing a target object in the characteristic position inside the tunnel, enabling a drive to drive a vehicle outside the tunnel towards the target object to obtain the visual cognition distance D within which the driver finds the target object, measuring the pavement brightness L20 of the position where the driver finds the target object, and calculating a brightness reduction coefficient K which is the ratio of L to L20; (d) resetting the average pavement brightness L of the tunnel portal section, and repeating the steps (b) and (c), so as to obtain multiple groups of different visual cognition distances D and corresponding brightness reduction coefficients K; (e) calculating and fitting data of multiple groups of D and K by using a Sigmoid function model, and calculating a relationship model formula (shown in the specification) of D and K; (f) substituting the safety parking visual distance D0 of the highest rate-limiting of the tunnel into the model formula, so as to obtain a smallest brightness reduction coefficient K0 of the tunnel portal section at day time. The invention further relates to a system for implementing the method.