The invention provides a multifunctional eight-claw robot for investigating manholes of an underground pipeline and an investigation method thereof. The multifunctional eight-claw robot is characterized in that a body is of a butterfly shape and comprises a walking module, cleaning structures, a control mechanism, a perception module, a power supply module and a joint driving system, wherein the walking module comprises bionic soles and foot parts, each foot part comprises three active joints, namely a hip joint, a knee joint and a ankle joint, the soles are connected with patella joints through ball hinges, and reset springs and foot mounting force sensors are arranged between the soles and the patella joints; the cleaning structures comprise shells, worm motors, cleaning hairbrushes, mechanical claws and cleaning steering engines; the control mechanism comprises a master control module, a data transmission module, an upper computer control module and a motor driving control module and adopts a hierarchical control system with a deliberative system framework; the perception module comprises a hazardous gas sensor, a first infrared sensor, a 360-degree rotary camera and an LED lighting lamps; and the power supply module adopts a special aviation lithium battery; and the joint driving system is driven by a fully-closed stepping motor. The invention further discloses a corresponding investigation method.