A stable positive corona discharge in coaxial electrode system withvarying humidity is analysed using a model which separates the corona in two distinctregions. A careful choice of boundary conditions in the drift region, particularly atthe cathode surface, is needed. A new method of current and electric fieldmeasurements with a linear biased probe, incorporated in the outer cylinder, is used.The corona current, at a given voltage, decreases with humidity but the electric field at the outer cylinder is independent of humidity. The fields at the surfaces of thecathode and the anode vary linearly with the applied voltage between electrodes. Theexact value of the average mobility of positive ions in the drift region is deducedfrom current and field measurements. This mobility increases when the potentialdifference across the drift region increases and it decreases slightly as the air ismade more humid. Other parameters of the positive corona are successively determinedby the current and field measurements, in particular, the total field distributionbetween electrodes.