The present invention provides a pixel circuit and a driving method thereof and a display device. The pixel circuit comprises a driving transistor, a storage capacitor, an organic light emitting device, a reset unit, a data writing unit and a voltage output unit. The reset unit is connected to a reset control signal line, an initialization signal line, the data writing unit, two ends of the storage capacitor, the voltage output unit, and a first electrode and a control electrode of the driving transistor. The control electrode of the driving transistor is connected to the second end of the storage capacitor, the first electrode thereof is connected to the voltage output unit, the second electrode thereof is connected to the organic light emitting device. The data writing unit is connected to a gate line, a data line and the first end of the storage capacitor.