The invention relates to an improved multi-tube serial avalanche tube Marx generator comprising a trigger unit and M levels of avalanche tube Marx circuits. The trigger unit is connected with the M levels of avalanche tube Marx circuits and is used for generating a trigger pulse and triggering to turn on a first avalanche tube of the first level in the M levels of avalanche tube Marx circuits; andthe M levels of avalanche tube Marx circuits comprise two preceding levels of circuits with auxiliary trigger and subsequent (M-2) levels of circuits in which bases are in short circuit with emitters, and are used for outputting high-voltage nanosecond pulses with repeated frequency. According to the improved multi-tube serial avalanche tube Marx generator provided by the invention, the two preceding levels of the M-level Marx generator are improved, and special circuit topology is designed, when the first avalanche tube of the first level is triggered to be turned on, an auxiliary trigger pulse is generated between the base and emitter of the second avalanche tube, so that the conduction state of the two preceding levels of avalanche tubes of the M levels of avalanche tube Marx circuitsis greatly improved.