Abstract: The effect of typhoon on the critical frequency of the F₂ region has been studied by using the observations made in 1969,1970,1972,1973.There are 21 observations of typhoon crossing or passing by Hainan chosen to compare with the simultaneous ionospheric data of the same area.It is found that there are evident correlations between the passage of the typhoon and the f₀ F₂.It is indicated that the f₀ F₂ decreases in the area right above the centre of the typhoon,but increases in the surrounding area.We suggest that the strong vertical convection in the troposphere caused by typhoon can change the local circulation system in the stratosphere and mesosphere,and this would influence the f₀ F₂ (e.g.number density of electrons in F₂ region) through the change of the height of the turbopause and the change of the ratio of atmospheric composition in the F₂ region.The result of this work shows that the study of the effect of the typhoon on the upper atmosphere is an applicable method for the research of the coupling between the upper and lower atmospheres.