Abstract: An estimation algorithm of reactor period for digital neutron monitoring system was studied based on Unscented Kalman filter (UKF), and the calculation algorithm of reactor period was given. The calculation results based on the simulation and experimental data were also given to verify the effectiveness of this algorithm. The results show that the UKF based algorithm for the estimation of reactor period is feasible and effective, and it can suppress the influence of measurement noise on calculation result to recover the signal’s original features.