A replacement method for scan cell of an integrated circuit (IC) is provided. A gate-level netlist of the IC is obtained. A place-and-route process is performed on the gate-level netlist to obtain a first netlist. A clock tree synthesis process is performed on the first netlist to obtain a second netlist. Static timing analysis is performed to analyze a plurality of first scan cells of the second netlist in normal mode and scan mode. The first scan cell is replaced with a second scan cell according to the static timing analysis that indicates the replaced first scan cell has a specific time margin in the scan mode. A first skew of the normal mode and a second skew of the scan mode are adjusted symmetrically in the first scan cell. The first skew and the second skew are adjusted asymmetrically in the second scan cell.