The present work establishes an integrated theoretical/numerical framework to study the characteristics of plasma enhanced H2-air counterflow diffusion flames. The oxidizer flow is activated by a parallel-plate nanosecond pulsed plasma discharge system with pulse duration ranging between 15 to 130 ns, and pulsing frequency between 5 to 60 kHz. The plasma discharge is modeled using a two-temperature model, with ions and neutral species in thermal equilibrium at the gas temperature, and electrons in thermal nonequilibrium. Electron transport and reaction rate coefficients are expressed as functions of mean electron energy, and stored in lookup tables. A large portion of input pulse energy is used in electron impact dissociation and excitation of N2 and O2. Plasma activation significantly increases the flame extinction strain rates, resulting in stable combustion even at lean conditions.