The energy transfer efficiency and energy dissipation of coupled piecewise linear stiffness energy sink are studied. The equation of systematic slow-varying equations of the two-degree-of-freedom system coupled with the piecewise linear stiffness ener gy is derived by the complex variable-averaging method under 1∶1 internal resonance. The approximate expression of two extreme points of the slow-invariant manifold is obtained by using the polynomial approximation method， and the energy transfer efficiency equation and energy dissipation equation of the coupled piecewise linear stiffness energy sink system are obtained. The effects of piecewise gap and piecewise linear stiffness on energy transfer efficiency and the relationship between damping coefficient of the main structure and dissipation time are analyzed. The results indicate that the energy transfer efficiency of the system decreases as the piecewise gap of the coupled piecewise linear stiffness energy sink increases， while it increases with an increase of piecewise stiffness. Additionally， it decreases with an increase of the damping system of the main structure. Therefore， adjusting structural parameters， the piecewise linear stiffness energy sink can effectively mitigate vibrations within the main structure.