Abstract: A hydraulic control system of a four-speed automatic transmission whereby second-to-fourth skip shifting or fourth-to-second skip shifting is possible. Line pressure is controlled variably to improve the power train efficiency and the response of shifting time during gear shifting. The exhaust port of the pressure control valve, which is controlled by the line pressure varying solenoid valve according to a duty ratio, is selectively opened to control line pressure. First and second pressure control solenoid valves are controlled according to a duty ratio such that the shift valves are controlled by drive pressure and speed line pressure.