A method for calculating an ionic electrical conductivity contribution percentage and electrical conductivity of a nutrient solution based on an ionic activity, characterized in that the method comprises the following steps: 1) calculating the ionic EC contribution percentage that is proposed and used to represent the contribution percentage of each ionic activity to the EC in the nutrient solution: EC i = Z i T i λ ∞ ∑ Z i T i λ ∞ × 100 wherein, EC i is the ionic EC contribution percentage of ion i, %; Z i is the charge number carried by the ion i; T i is the ionic activity of the ion i, mol/L; and λ ∞ is the limit equivalent ionic conductivity of the ion i, m 2 S/mol; 2) calculating the ionic activity which represents an effective concentration of the ion that plays a role in electrolyte solution and is a concentration of an ion that plays an electrostatic role in the nutrient solution: T i = γ i C i wherein, T i is the ionic activity of the ion i, mol/L; γ i is the ionic activity coefficient of the ion i; Ci is the ionic concentration of the ion i, mol/L; 3) calculating the mean ionic activity that represents comprehensive concentration or comprehensive activity of the ions in a single salt solution or a mixed solution: T = T i v i ⋅ T j v j 1 v i + v j wherein, T is the mean ionic activity of a single salt solution or a mixed solution, mol/L; T i and T j respectively are the ionic activities of the cations and the anions constituting the single salt solution or the mixed solution, mol/L; v i and v j respectively are the number of the cations and the anions constituting the single salt solution or the mixed solution; 4) calculating, by Debye-Hiickel limiting equation applicable to characteristics of the nutrient solution, the ionic activity coefficient that is a correction coefficient representing deviation between an actual solution and an ideal solution: − lg γ i = AZ i 2 I 1 + Br i I wherein, y; is the ionic activity coefficient of the ion i; A is a constant related to temperature, 0.5091 at 25°C; B is a constant related to ionic size, 0.328 at 25°C; Zi is the charge number carried by the ion i; r i is a volume parameter of the ion i; I is ionic strength of the nutrient solution, mol/L; 5) calculating the ionic strength that represents the electric field strength caused by the ions present in the nutrient solution: I = 1 2 ∑ C i Z i 2 wherein, I is the ionic strength of the nutrient solution, mol/L; C i is the ionic concentration of ion i, mol/L; Z i is the charge number carried by the ion i; 6) measuring the EC and pH of the nutrient solution; 7) based on the mean ionic activities T of each single salt in the nutrient solution, estimating the EC of the nutrient solution by multivariate linear regression models, and inversely calculating the ionic concentration by using the actually measured EC and ionic EC contribution percentage. 1) calculating the ionic EC contribution percentage that is proposed and used to represent the contribution percentage of each ionic activity to the EC in the nutrient solution: EC i = Z i T i λ ∞ ∑ Z i T i λ ∞ × 100 wherein, EC i is the ionic EC contribution percentage of ion i, %; Z i is the charge number carried by the ion i; T i is the ionic activity of the ion i, mol/L; and λ ∞ is the limit equivalent ionic conductivity of the ion i, m 2 S/mol; 2) calculating the ionic activity which represents an effective concentration of the ion that plays a role in electrolyte solution and is a concentration of an ion that plays an electrostatic role in the nutrient solution: T i = γ i C i wherein, T i is the ionic activity of the ion i, mol/L; γ i is the ionic activity coefficient of the ion i; Ci is the ionic concentration of the ion i, mol/L; 3) calculating the mean ionic activity that represents comprehensive concentration or comprehensive activity of the ions in a single salt solution or a mixed solution: T = T i v i ⋅ T j v j 1 v i + v j wherein, T is the mean ionic activity of a single salt solution or a mixed solution, mol/L; T i and T j respectively are the ionic activities of the cations and the anions constituting the single salt solution or the mixed solution, mol/L; v i and v j respectively are the number of the cations and the anions constituting the single salt solution or the mixed solution; 4) calculating, by Debye-Hiickel limiting equation applicable to characteristics of the nutrient solution, the ionic activity coefficient that is a correction coefficient representing deviation between an actual solution and an ideal solution: − lg γ i = AZ i 2 I 1 + Br i I wherein, y; is the ionic activity coefficient of the ion i; A is a constant related to temperature, 0.5091 at 25°C; B is a constant related to ionic size, 0.328 at 25°C; Zi is the charge number carried by the ion i; r i is a volume parameter of the ion i; I is ionic strength of the nutrient solution, mol/L; 5) calculating the ionic strength that represents the electric field strength caused by the ions present in the nutrient solution: I = 1 2 ∑ C i Z i 2 wherein, I is the ionic strength of the nutrient solution, mol/L; C i is the ionic concentration of ion i, mol/L; Z i is the charge number carried by the ion i; 6) measuring the EC and pH of the nutrient solution; 7) based on the mean ionic activities T of each single salt in the nutrient solution, estimating the EC of the nutrient solution by multivariate linear regression models, and inversely calculating the ionic concentration by using the actually measured EC and ionic EC contribution percentage.