Abstract: The prompt decay constant α has significant application on the physical design and safety analysis in nuclear facilities. To overcome the difficulty of α value calculation with Monte-Carlo method, and improve the precision, a new method based on the neutron noise analysis technology was presented. This method employs the stochastic simulation and the theory of neutron noise analysis technology. Firstly, the evolution of stochastic neutron was simulated by discrete-events Monte-Carlo method based on the theory of generalized Semi-Markov process, then the neutron noise in detectors was solved from neutron signal. Secondly, the neutron noise analysis methods such as Rossi α method, Feynman α method, zero-probability method, and cross-correlation method were used to calculate α value. All of the parameters used in neutron noise analysis method were calculated based on auto-adaptive arithmetic. The α value from these methods accords with each other, the largest relative deviation is 7.9%, which proves the feasibility of α calculation method based on neutron noise analysis stochastic simulation.