Abstract: ⁹⁰Sr is a pure β decay nuclide, but because its decay progeny ⁹⁰Y half-life is only 64 hours, it will have an impact on the accurate determination of ⁹⁰Sr activity, given its own nature, the analysis method of ⁹⁰Sr is relatively complex, the liquid scintillation triple-to-double coincidence ratio method (TDCR) is used to measure the ⁹⁰Sr radioactivity activity, in the state of equilibrium of the ⁹⁰Sr-⁹⁰Y daughter. The total counts of ⁹⁰Sr and ⁹⁰Y were measured, and the calculation of the total TDCR efficiency will be calculated according to the sum of the two nuclide efficiencies. The calculation of the TDCR efficiency was first performed by using the BataShape program to calculate the ⁹⁰Sr and ⁹⁰Y energy spectra, and the efficiency of counting β-particles in the scintillating liquid based on the free-parameter model by using the efficiency calculation program written and obtaining the efficiency curves of ⁹⁰Sr/⁹⁰Y, combined with the experimental results of the TDCR values and efficiency curves are combined to achieve the absolute measurement of ⁹⁰Sr activity with a relative standard uncertainty of 0.36%, which provides a reliable tool for environmental monitoring and nuclear safety fields.