Abstract: Ionospheric f_min is the lowest echo frequency observed on the frequency height map, which is an important index of the performance of the ionosonde and also an important index for the study of the absorption effect in the ionospheric D region. In this paper, the ionospheric absorption intensity, spatial distribution, diurnal variation, seasonal variation and long-term variation are studied by using ionospheric f_min data from Xi’an, Urumqi and Lanzhou stations of China ionospheric vertical survey network in the Northwest Corridor region. The study of ionospheric absorption variation is of great application value to the selection of the lowest frequency of shortwave communication, the evaluation of detection performance of sky-wave over-the-horizon radar and the prediction of VLF telecommunication efficiency. At the same time, ionospheric absorption is closely related to the electron density of the D layer, which is an important indicator of the intensity of the electron density of the D layer. To study the ionospheric absorption characteristics is of great scientific significance for the study of the ionospheric variation characteristics and the establishment of the electron density distribution model in the D region. The absorption effect of ionospheric region D in the Northwest Corridor mainly occurs in the daytime, with the highest absorption intensity at noon and the weakest in the early morning at night. Meanwhile, the absorption effect of ionospheric region D in the Northwest Corridor has significant seasonal variation characteristics, the strongest in summer and the weakest in other seasons. The ionospheric f_min value of Urumchi at higher latitude is obviously higher than that of Xi’an and Lanzhou at middle latitude, and the absorption effect center has obvious diurnal drift characteristics. The absorption of ionospheric region D in the Northwest Corridor is positively correlated with the intensity of solar activity. In particular, the absorption intensity of ionospheric region D in high solar activity years is significantly higher than that in low solar activity years.