A calculation method of illumination standard for a tunnel entrance section in daytime based on safe visual recognition, comprising the following steps: Step-ao: setting average road surface brightness of the tunnel entrance section to be L; Step-co: measuring a brightness L 20 outside the tunnel, and calculating a brightness reduction factor to be a ratio between the average road surface brightness of the tunnel entrance section L and the brightness outside the tunnel L 20; Step-fo: obtaining a minimum brightness reduction factor K 0 of the tunnel entrance section in daytime; characterized in that, the method further comprises: Step-a: setting a color temperature of the tunnel entrance section to be T 0, and setting a color rendering index of the tunnel entrance section to be R a0; Step-b: determining a feature position in the tunnel where the road surface brightness in the tunnel begins to remain constant; Step-c: measuring a visual recognition distance required by a driver to visually discover a target object placed at the feature position in the tunnel when driving at various speeds from outside the tunnel towards the target object; Step-d: resetting the average road surface brightness L of the tunnel entrance section and repeating the Step-b, Step-co and Step-c to obtain a plurality of sets of visual recognition distances D and corresponding brightness reduction factors K associated with the respective average road surface brightness; Step-e: based on the obtained plurality of sets of visual recognition distances D and corresponding brightness reduction factors K, using a Sigmoid function model to calculate and fit the data of the plurality of sets of D and K to obtain a relational model formula of D and K; wherein said Step-fo of obtaining a minimum brightness reduction factor K 0 of the tunnel entrance section in daytime comprises Step-f of substituting a safe stopping sight distance D 0 corresponding to a maximum speed limit designed for the tunnel into the relational model formula. Step-ao: setting average road surface brightness of the tunnel entrance section to be L; Step-co: measuring a brightness L 20 outside the tunnel, and calculating a brightness reduction factor to be a ratio between the average road surface brightness of the tunnel entrance section L and the brightness outside the tunnel L 20; Step-fo: obtaining a minimum brightness reduction factor K 0 of the tunnel entrance section in daytime; Step-a: setting a color temperature of the tunnel entrance section to be T 0, and setting a color rendering index of the tunnel entrance section to be R a0; Step-b: determining a feature position in the tunnel where the road surface brightness in the tunnel begins to remain constant; Step-c: measuring a visual recognition distance required by a driver to visually discover a target object placed at the feature position in the tunnel when driving at various speeds from outside the tunnel towards the target object; Step-d: resetting the average road surface brightness L of the tunnel entrance section and repeating the Step-b, Step-co and Step-c to obtain a plurality of sets of visual recognition distances D and corresponding brightness reduction factors K associated with the respective average road surface brightness; Step-e: based on the obtained plurality of sets of visual recognition distances D and corresponding brightness reduction factors K, using a Sigmoid function model to calculate and fit the data of the plurality of sets of D and K to obtain a relational model formula of D and K; wherein said Step-fo of obtaining a minimum brightness reduction factor K 0 of the tunnel entrance section in daytime comprises Step-f of substituting a safe stopping sight distance D 0 corresponding to a maximum speed limit designed for the tunnel into the relational model formula.