Abstract: The measurements of HF Doppler shift in the ionosphere have long been a powerful tool in monitoring the ionospheric disturbances due to its features of continuity in time and simplicity. In this paper, based on the analysis of data from the HF Doppler station at Peking University, some typical records with special morphological characteristics of the ionosphere were shown. These records are recognized as the manifestations of sporadic-E, irregularities, acoustic-gravity waves in different scales and response to the sudden change of electron density due to solar flares. Using IRI model of the ionosphere, responses of Doppler shift to solar flare and ionospheric irregularities are simulated. The results are in agreements with observations so that the mechanics of such physical processes are explained. A special kind of records——"S" shaped trace is introduced and programs designed to simulate such records. It is shown that the "S" shaped traces are produced by horizontally propagated acoustic-gravity waves under proper conditions. Relations between shapes and AGW's parameters are also given. These results are helpful in deducing some properties of AGWs from Doppler shift records.