Abstract: Based on the researches of the event alarm logic of loose parts and worldwide regulations and standards of loose parts event alarm and emergency response, combined with the loose parts event alarm and emergency response in a domestic nuclear power plant during hot state function test, the process of a  loose part event in that nuclear power plant is analyzed in detail. The loose parts event alarm is divided into absolute and relative threshold alarms. To improve the alarm accuracy, counting factor and channel rechecking are increased in the alarm logic. GB/T 11807, IEC 60988 and ASME require to take measures to determine if the event alarm is caused by the loose parts, and the potential damage to the primary loop system of the reactor is evaluated by the loosen parts. RG 1.133 requires that the loose event alarm should be reported to the Nuclear Regulatory Commission. GB/T 11807 and IEC 60988 have no clear specification on whether the loose part events should be reported to the national nuclear safety administration, which is determined according to the specific operation of the nuclear power plant. Based on the alarm and emergency response to a loose part event in a nuclear power plant in China, it is suggested that the emergency response mechanism suitable for nuclear power plants in China should be established, loose parts events should be determined in time, and the possible loss of equipment components should be evaluated timely, and further provisions should be made on whether to report and take what measures.