Abstract: The hourly value of horizontal component of geomagnetic field measured in Trivandrum, India has been analysed.The data length covers about two sunspot cycles.After reducing the variations of solar cycle and one year periodity in the data set,a quasi-biennial variation in the occurrence of Counter Electrojet(CEJ) is revealed:the occurrence of CEJ is increased in the easterly phase of QBO and decreased in the westerly phase of QBO. Based on this discovery,the causative mechanism of CEJ is discussed.It is suggested that, the interaction between the upward propagating planetary waves and solar and lunar semidinal tides,may causes the semidinal tides enlarging in amplitude and shifting in phase, and finally results in the occurrence of CEJ.