The invention relates to a sampling assembly for detecting a pH value of a polymerization kettle. A sampling opening is disposed at an outlet of a filter; an inlet shutoff valve is connected with the sampling opening; one end of a pressure sampling device is connected with the inlet shutoff valve; the other end of the pressure sampling device is connected with an inlet of a circulation bracket; an outlet of the circulation bracket is connected with an outlet shutoff valve; one end of the circulation bracket is provided with an open flange; the other end of the circulation bracket is provided with a sensor installation opening; a pH transmitter is fixed on the circulation bracket through an installation fixing end cover of the sensor installation opening; an outlet of the outlet shutoff valve is connected with a termination tank through a reflux pipleline; one end of the pressure sampling device is provided with an installation flange; the other end of the pressure sampling device is sealed; a pressure transmitter is mounted on the pressure sampling device; the pH transmitter is connected with a pH controller; the pH controller is connected with a control valve and a flow transmitter; one end of the control valve is connected with the flow transmitter; and the other end of the control valve is communicated with the polymerization kettle. The assembly is small in maintenance amount, convenient for maintenance, low in failure rate and convenient for disassembly. A probability that a detection chamber of the sensor is blocked by polymer is greatly reduced.