<p>Since the passive nuclear power plant is not equipped with a boron recovery system, in order to minimize the amount of waste liquid generated by sampling, the inner diameter of the sample lines is usually small and the Grab Sample Panel is compact, which leads to the problem that the sample lines is easy to be blocked. The number of Containment Penetrations has greatly reduced to 2 for 11 liquid sample sources in passive nuclear power plant, which makes sample liquid vulnerable to the influence of other sample fluids, thus resulting in low sampling representativeness. In view of the problems, we have taken the following design optimization. First, a Spare Glove Box has been added to ensure the PSS sampling function when the MS20 is not available. The box is arranged in room 12152 of the auxiliary building, and two interfaces reserved to the radiological chemical laboratory were connected to it. It is connected in parallel and standby with the Grab Sample Panel. It can be used to obtain liquid and/or Containment atmosphere sample. Second, according to the characteristics of the sampling sources, the sample lines shall be reasonably separated, and the shared pipeline shall be reduced or avoided as far as possible to improve the representativeness of sampling. The liquid sample lines in the Containment joins into five sample lines, and three Containment Penetrations shall be added accordingly. Multiple isolation valves shall be set on the sample lines of a single sample point to avoid internal leakage and cross flow during the sampling process. Third, the other optimization measures also will be implemented. For example, the inner diameter of sample lines is increased, while the outer diameter of the sampling piping remains unchanged. The measure of added a Spare Glove Box has been successfully applied to the four operating units in China and have good results. The other measures have not been implemented, which will be applied to the subsequent new NPPs. The paper introduced the optimization measures to improve the convenience of PSS operation and maintenance and lower personnel radiation dose. It is a reference for other passive NPPs.</p>