Based on the shaping characteristic of femtosecond in the focal region and the free electron density rate equation, through modifying the electron diffusion rate and cascade ionization rate, the ellipsoidal time and space (ETS) model for femtosecond laser-induced optical breakdown in water was given. Theoretical breakdown thresholds calculated by ETS model with a Runge-Kutta method were presented under the condition of pulse durations of 100 fs and 300 fs. The optical breakdown thresholds and the electron distribution within the breakdown region at different times were given, and the change of free electrons with time at fixed positions within the region was predicted. Results show that the breakdown threshold of water induced by femtosecond laser using the ETS model is better agreement with experimental result than the classical models.