The single-phase T-type three-level inverter is firstly applied to the electric spring with switchable smart load, which reduces the harmonic content of the load voltage and a mathematical model of the T-type three-level electric spring with switchable smart load is established. And, the influence of the traditional carrier modulation on the mid-point potential of the T-type three-level electric spring with switchable smart load on the DC side is derived, and the control scheme of the mid-point potential is introduced, which combines with the integral separation control idea to obtain the control strategy of the T-type three-level electric spring with switchable smart load. The control strategy can effectively reduce the overshoot of the load voltage during the fluctuation of the grid voltage. Finally, it is verified by Matlab/Simulink simulation that the improved harmonic content is reduced by 3.47% and 1.65%, and the overshoot is reduced by 0.34%and 0.1% when stabilizing the critical and non-critical load voltages.