A modularized-reconfigurable long-term in-situ monitoring device, comprising a fixed component, wherein the fixed component is provided with a physical and chemical parameter sensor interface, a multi-channel Raman detection system, a camera system, an ocean current recording system, a control system, a power supply system, a lighting system, a floating body and an optical communication system, a releaser is arranged in the middle of the top of the fixed component, the releasing end of the releaser is connected with one end of a connecting rod penetrating through the fixed component, and the other end of the connecting rod is connected with a bottom counterbalance weight through a manual releaser.