Abstract: The sodium column abundance and the peak density height of the twilight sodium layer are measured with a narrowband filter photometer from 19 twilightglow observations at the northern suburbs of Beijing between March 1987 and January 1990. It is shown that there are higher layers in spring and summer and lower layers in autumn and winter. The layer thickened in winter. The average height of the peak density is 85.7km for eight winter evenings. An annual variation by a factor of 7.5 in the sodium column abundance with maximum in winter is observed. The height and concentration variations of the sodium layer are triggered not only by the sodium photochemistry, but also by some dynamic processes.