The invention discloses a cascade type optical cable monitoring method based on an optical time division technology. The method is characterized in that monitoring light is emitted by one instrument through an optical switch, and the monitoring light is sent to corresponding ports at different time intervals; a first-stage optical switch is cascaded below each output port; the smaller time interval is distributed to the transmitted monitored light to the corresponding output ports again, by analogy, one comprehensive monitoring instrument carries out polling type or roll-call type monitoring on different optical cables of different substations at different time buckles through an optical switch cascading mode, so that the use efficiency of the instrument is greatly improved. The monitoringmethod can be applied to an online optical cable monitoring system, and the system construction cost and the operation and maintenance cost are reduced, a large number of optical cables can be conveniently and efficiently monitored, and the operation and maintenance working efficiency and the management level of the optical cables can be improved.