Drum filter is a large-scale filtration equipment in nuclear power plants, providing clean cooling water for nuclear power plants. At present, there are problems of easy blockage, short response time of the unit after blockage, and shutdown of the unit in severe cases during the operation of the drum filter in the in-service nuclear power plants. The analysis shows that the drum filter adopts the structure of “internal water intake”, and the garbage such as marine organisms remain on “inside” of the drum filter during operation, which makes it difficult to clean up and operate the inner garbage. When the marine organisms suddenly break out, if the amount of garbage cleaned by the drum filter is not enough to offset the amount of garbage entering, the garbage will accumulate continuously inside, which may lead the pressure difference between the inside and outside of the drum filter to suddenly increase, and then cause the circulating pump to trip or even the reactor to shut down. The inherent safety of the drum filter of this water intake method is low. To solve this problem, this paper puts forward a new concept of water intake of drum filter, that is, the concept of “external water intake”, which changes the water intake method of the drum filter, intercepts the garbage on the “outside” of the drum filter. Under the action of water flow, the garbage outside is not easy to remain on the net and block the drum filter, thereby fundamentally improving the inherent safety of the drum filter. A new type of “external water intake” drum filter was developed by using parametric and modular design method. The reliability of the drum filter was analyzed by using the FMEA failure mode and impact analysis method, and the weak links of the drum filter were found out, and optimization and improvement measures have been taken for the weak links. The ANSYS finite element analysis software is used to conduct a seismic analysis of the drum filter, which proves that the drum filter meets the requirements of the RCC-M specification and the seismic requirements of the third-generation nuclear power plants, which demonstrates the safety of the drum filter. Finally, through the physical prototype test, the design concept of “external water intake” was verified, and garbage cleaning capacity of the new drum filter meets the requirements of nuclear power plants. This type of drum filter has been popularized and applied to many HPR1000 projects under construction and newly built ones.