Abstract: System strength reflects the support capability of AC systems for connected devices. With the increasing of power electronics, a shift towards high-penetration power electronics systems has emerged, altering the traits of power systems dominated by synchronous machines. However, the weak support, low disturbance resistance and high flexibility of power electronics have gradually changed the system strength. Accordingly, this paper proposes the definition of strength of power system integrated with high penetration of power electronics. It proposes a classification method for supporting strength and regulating strength based on the dynamic response characteristics for frequency and voltage stability modes, establishing a fundamental system strength framework. For supporting strength, the generalized inertia and inertia disturbance ratio serves as the index, while the short-circuit ratio and impedance ratio serve as the voltage supporting strength indexes. For regulating strength, sensitivity indicators for frequency/voltage fluctuations are established separately. Finally, several key technologies for enhancing system strength are introduced. These findings will provide support for ensuring the safe, stable, and efficient operation of power systems and achieving the "dual carbon" goal.