The invention discloses a device and a method for focusing a cold plasma to process a 3D object. The device comprises a jet flow support, dielectric barrier tubes, tungsten electrodes, a support shaft, a mobile mechanical arm, a sample fastener, a gas circuit chamber and a line chamber, wherein the cross section of the jet flow support is a regular polygon cylinder and a vertical through hole is arranged at the center position of a thickness direction; there are several dielectric barrier tubes, and one end of each dielectric barrier tube passes through the side surface of the corresponding jet flow support and is inserted into the vertical through hole of the jet flow support; the tungsten electrodes are fixedly arranged at the central axes of the dielectric barrier tubes, and the numberis the same with the number of the dielectric barrier tubes; the support shaft is vertically arranged at one side of a jet flow array; one end of the mobile mechanical arm is movably connected to thesupport shaft, and the other end of the mobile mechanical arm is connected to the sample fastener; the lower end of the sample fastener is provided with an insulation clamping structure used for clamping a sample to be processed; and the uniform cross sections of the gas circuit chamber and the line chamber are regular-polygon hollow cylinders, the gas circuit chamber is arranged on the upper endof the line chamber, and the jet flow support is nested in the gas circuit chamber.