The invention discloses an underground water online monitoring and representative water sample collection integral self-control device and a control method thereof and relates to the technical field of underground water monitoring and water sample collection. The device comprises a control operation station, a representative water sample judgment collection system and an online in-situ monitoringsystem, wherein the control operation station is arranged on the ground; the online in-situ monitoring system is connected with the control operation station and is arranged under an underground waterlevel in a well; the online in-situ monitoring system is connected with a water pump under the underground water level through a tube; the water pump is connected with a stagnant water collector anda water sample collector through tubes; an online spectrum water quality monitor II and a common parameter water quality analyzer II of the online in-situ monitoring system are used for monitoring andanalyzing water inside the stagnant water collector and the water sample collector. To ensure that fresh water samples of water layers are monitored, and water samples are collected in multiple dimensions from multiple sites to stably judge water sample representativeness according to water quality parameters. Integration of monitoring and sampling techniques is deepened, and in-situ informationacquisition uncertainty is greatly reduced.