X-ray detection technology enriches the existing methods of detection of temporary sources, and is an important objective of current space science research. In order to achieve high reliability, fully autonomous early warning and follow up of soft X-ray transient sources on orbit, and get rid of dependence on ground data processing, the WXT payload spaceborne trigger unit of Einstein probe satellite developed by the Chinese Academy of Sciences implemented an on orbit transient source search trigger algorithm, calculated the celestial location of the source in real time, and triggered the satellite platform to perform a follow up observation after maneuvering. This paper introduces the method design of the spaceboard trigger unit autonomous search and warning followed observation in detail, and proves the ability of real-time and rapid data processing through ground tests and on orbit operation. Spaceborne triggering units provide key technology assurance for the Einstein Probe Project to achieve high sensitivity, large field of view sky survey observations in the soft X-ray band, introducing scientific exploration into vast unknown spaces, revealing more of the mysteries of the universe for humanity.