The invention provides an apparatus for acquisition of marine sediment porewater and on-line in-situ detection of gas in the porewater. The apparatus can realize in-situ, rapid and cyclic acquisition of the porewater and on-line in-situ detection of the composition and content of gas in the porewater. According to a technical scheme in the invention, the apparatus is characterized by comprising a counterweight (1), a shell (2), a gas cylinder (17) and a single-layer sampling point device (13), wherein the counterweight (1) is connected with the shell (2), the counterweight (1) is provided with a power supply and a signal path device (18), and the gas cylinder (17) and the single-layer sampling point device (13) are arranged in the shell (2) and connected with each other. The invention also discloses a control method for the apparatus.