The transient process of the programming and erasing is very important for a nanocrystal-floating-gate flash memory. In this work, a computer simulation was carried out to investigate the charging, retention and erasing processes of our proposed Ge/Si hetero-nanocrystal floating gate flash memory. The transient gate current, the transient drain current and the average charge in one dot were simulated respectively. Evident hysteresis features can be observed in the transient processes in a voltage-sweeping measurement mode. While measuring the transient process in a constant voltage mode, the time decay of transient current and charge are weakened if Ge is used on the Si dot, indicating a longer retention time for Ge/Si-floating-gate flash memory.