Estimating the latency time of the clock tree of an ASIC including: providing a netlist and a placement related to the clock tree of the ASIC; extracting a number of the load timing devices connected by the clock tree according to the netlist related to the clock tree; extracting a physical distribution area of the load timing devices connected by the clock tree according to the placement related to the clock tree; estimating a latency time of the clock tree according to the relationship between the number of the load timing devices, the physical distribution area of the load timing devices and latency time of the clock tree in design data related to the ASIC design.