Disclosed are a pixel circuit, a drive method thereof and a display panel. The pixel circuit includes: a discharge module, a storage module, a comparison module, and a drive module. The drive module is configured to drive, according to a voltage outputted through the output end of the comparison module, a light-emitting module to emit light. In a light-emitting phase, the discharge module discharges the storage module; and the comparison module compares an input voltage received from the first input end with a reference voltage received from the second input end and outputs, to the control end of the drive module, a constant voltage for turning on the drive module or a voltage for turning off the drive module, so that the drive module generates a constant drive current when being turned on.