The viscoelastic properties of cells reflect their biological behaviors and disease states, and are usually calculated based on atomic force microscope (AFM) indentation curves. But the indentation scenario of cells using AFM probes does not conform to the assumptions of the Hertz model, incurring errors of the calculated values. The existing correction models primarily address small deformation errors, and the failure of the semi-infinite space assumption due to the finite spreading area of cells is largely ignored. In response, we here propose a corrected model based on finite element data, validated by simulations and indentation experiments. This model eliminates errors from both Hertz assumptions, enabling accurate extraction of viscoelastic parameters such as elastic modulus and apparent viscosity.