In offshore oil field in China, negative pressure perforating or balanced perforating with negative pressure flowback technology is often adopted to reduce the pollution of reservoir during perforating operations. However, the influence of string structure on actual effective negative pressure value is not considered in current operations, and sometimes complicated accidents may be caused by downhole tools during operations. Based on the commonly used negative pressure string structure, this paper calculated and analyzed the influence of RTTS packer position, negative pressure valve depth, drill pipe casing size and other factors on effective negative pressure value. On the premise of meeting the requirements of negative pressure, raising the position of the negative pressure valve moderately has little effect on the effective negative pressure value. The feasibility of using annular blowout preventer instead of RTTS packer and reducing the depth of negative pressure valve was researched. Compared with the traditional scheme, the improved negative pressure operating string has no RTTS packer, and the well deviation is low in negative pressure valve position, which simplifies the operation process and is conducive to improving the field operation efficiency.