Abstract: In accelerator-driven subcritical system (ADS), the transient characteristic is quite different from that of traditional critical system due to its strong external neutron source and its fuel composition for transmutation. This paper presents a coupled stochastic-deterministic method for analysing the transient characteristic of ADS. After comparing various reactor transient calculation methods, predictor-corrector improved quasi-static method was chosen to handle the time variable of neutron space-time kinetics equation. Considering the specific neutron spectrum, Monte Carlo method was used to handle the corresponding spatial, angle and energy variables. The main problem encountered is the Monte Carlo iteration instability for slightly subcritical system. Numerical results demonstrates the effectiveness of the new method.