The invention relates to a pipe orifice variable plug-in type sampling instrument. The pipe orifice variable plug-in type sampling instrument structurally comprises taper pipes, a straight pipe, a steady flow buffer pipe, a core pipe, a flow-dividing pressure regulating valve, a pressure gauge, a sampling hose, a concentric type flow regulator and the like. The sampling instrument provided by the invention changes the composition, the structure and the working principle of an original organic matter polluted water sample collecting device, and has the characteristics of small size, light weight, wide application range, convenience for carrying and installing, simplicity in operation, safe use, avoidance of polluting a sample in the collecting process, etc., so that the fidelity of the collected sample is increased, the sample collecting cost is lowered, the safety of staffs and equipment is guaranteed, and the universality of the sampling instrument is improved.