The invention relates to a single-unit single-acting-cylinder metering pump car posture regulating system which is composed of a main pressure control valve unit for a metering pump, a first left load-sensitive proportional throttle valve unit for a single acting cylinder, the metering pump and a first left hydro-pneumatic suspension. The main pressure control valve unit for the metering pump and the first left load-sensitive proportional throttle valve unit for the single acting cylinder are sequentially connected in series between the metering pump and the first left hydro-pneumatic suspension, and the loaded pressure feedback control end of the first left load-sensitive proportional throttle valve unit for the single acting cylinder is connected with the control end of the main pressure control valve unit for the metering pump, so that the oil inlet pipe pressure of the system is always 0.6 Mpa-0.9 Mpa higher than the loaded pressure.