Abstract: Difference from the movable neutron detector for CPR1000 reactor can only be used periodically, HPR1000 and other Gen-Ⅲ reactor innovatively use self-powered neutron detector (SPND) to continuously measure the in-core neutron flux. This paper provided detailed design and implementation of the high-precision core surveillance system for the first HPR1000 reactor. Firstly, a novel SPND signal processing method was proposed, which not only solved the limitation of traditional design software for high-precision SPND current calculation, but also enabled high-precision signal processing of measured SPND. Based on this, a high-precision core 3D power reconstruction method was established. Subsequently, the online monitoring system SOPHORA for the HPR1000 reactor core designed based on this theoretical model was described, and its uncertainty analysis method was explained in detail. The uncertainty analysis results indicate that the accuracy of the key parameters of the system can meet the needs of high-precision core monitoring. Finally, in order to confirm the performance of the system, a comparative analysis was conducted on the deviation between the measurement and theoretical prediction of SPND current during the start-up process of the HPR1000 reactor, as well as the deviation of component power distribution. The results show that the deviation is much smaller than the regulatory requirements for initiating physical tests. The double validation of the uncertainty analysis results and the component power deviation analysis results during the start-up process indicates that SOPHORA achieves high-precision core monitoring, and its use of SPND signal processing and core 3D power reconstruction methods has significant accuracy and reliability.