The operation of diffusion step recovery diodes (dSRD) as current interrupters in high-power nanosecond pulse generators was studied in detail by the methods of numerical computer simulation for the first time. One of the necessary conditions that minimize the loss in dSRD was specified. Dependences of pre-pulse voltage, front duration, amplitude and duration of pulse formed on the active load, and the energy of switching losses in the dSRD on the device area and the break current density are obtained. It is shown that simulation results can be described by simple analytical formulas obtained in the second part of the work, with an accuracy of 10-20% if the pulse amplitude does not exceed the avalanche breakdown voltage of the dSRD. The generalized figure of merit which can be used for optimization of dSRD parameters, a mode of its operation and comparison of efficiency of current interrupters of various types was offered.