The invention designs a three-connecting-rod type marine self-grabbing and releasing mechanical arm device capable of actively controlling constant tension. The device mainly comprises a base, a balance platform, a left balance arm, a right balance arm, a tension sensor, a first connecting rod, a second connecting rod, a third connecting rod, a left auxiliary balance arm, a right auxiliary balancearm, a main sling, a left balance cable, a right balance cable, a left auxiliary balance cable, a right auxiliary balance cable, a visual sensor, a lifting ring, a grab hook and a PLC control box. Four balance cables are adopted, active constant
tension control is achieved through a PLC, and automatic grabbing, collecting and releasing functions are achieved through the grab hook of the visual sensor. The device has the advantages that a multi-degree-of-freedom three-connecting-rod type mechanical arm is used, and the grabbing range is enlarged. Meanwhile, the influence of marine
environmental factor interference force on the main sling, the grab hook and the hoisted object is considered. The four balance cables are adopted, so that the stabilization effect is improved. The visual sensoris applied, the marine mechanical arm can automatically grab, collect and release the hoisted object, and compared with a manually-operated marine crane, the device is more intelligent and suitable for various carriers.