The spin-forbidden predissociation reaction of the ground state N2O is studied by quantum dynamics calculations. Ab initio calculations are carried out to obtain the potential energy surfaces (PES') of the singlet ground state of N2O and three triplet ones correlating with the asymptote N-2+O(P-3) and the spin- orbit coupling (SOC) elements among them. The decay rate of individual singlet vibrational state to the (3)A' state are estimated by applying Fermi golden rule. For the (1)A' state, totally 1692 vibrational eigenstates with the even parity for the total angular momentum J = 0 are obtained, and time-dependent wave packet calculations on the triplet PES are performed to obtain the autocorrelation functions whose Fourier transforms provides the decay rates. The resultant decay rates for 887 singlet vibrational states in the energy range 67.3 less than or equal to E less than or equal to 83.7 kcal/mol are analyzed in terms of a random matrix/transition state theory. Incomplete energy randomization of the vibrational energy in the singlet state even near the singlet state dissociation threshold is concluded from the analyses of calculated decay rate distributions.