Low-injection energy electrons are accelerated in a continuous standing wave linear accelerator. Electron flow is supplied directly from a low-energy electron source to subsequent sequential accelerating units interconnected via connection cells. By grouping electrons in the first bunch resonator at a determined gap voltage, increasing the electron energy in a booster resonator and accelerating the electron energy in the accelerating unit, the optimal phase of particles with respect to the electromagnetic field is ensured. The length of each accelerating structure segment, which is located between centers of the adjacent cells, is based on the equality between the relation of the length of each following segment to the length of the previous segment and the relation of the average electron speed in the previous segment to the average electron speed in the following segment.