The invention provides a tunnel ventilating system and method. The tunnel ventilating system comprises a draining tunnel, a left line, a right line, a parallel adit, a total intake airflow roadway, atotal return airflow roadway, a plurality of left cross roads and a plurality of right cross roads. The total intake airflow roadway is connected with the right line and the draining tunnel, and the total return airflow roadway communicates with the left line. A left road communicates with the parallel adit and the left line, and a right road communicates with the parallel adit and the right line.An air chamber is formed in the communicating position of the total intake airflow roadway and the right line. The tunnel ventilating method comprises the steps that the first excavation face of theparallel adit, the left excavation face of the left line and the right excavation face of the right line are constructed, and the first excavation face of the parallel adit is constructed by a presetdistance in advance relative to the left excavation face of the left line and the right excavation face of the right line; the left road communicating with the parallel adit and the left line is formed between the two left cross roads, and the right road communicating with the parallel adit and the right line is formed between the two right cross roads; and a front air partition moves forwards toprolong the air chamber. The air chamber is prolonged forwards by stages, the pressure of one-time long-distance ventilation is relieved, and the ventilation efficiency is improved.