In an injection pressure control method of a GDI engine, an engine torque and an engine rpm are detected, then an initial stratified mode fuel pressure value is set according to the detected engine torque and engine rpm. Next, a weighting factor is calculated according to a variation rate in effective pressure of a combustion chamber of the engine, and a corrected stratified mode fuel pressure value is established by multiplying the wighting factor to the initial stratified mode fuel pressure value. Then, the corrected stratified mode fuel pressure value is compared with a current fuel pressure value, then a final fuel pressure value is obtained according to the comparision result.