Abstract: In this paper, experimental formulae of the critical frequencies of the E-layer in mid-latitudes and of the distribution of electron density in the lower ionosphere are found. These formulae are expressed in terms of the sunspots number, the solar zenith angle and the local time. The results of calculations from them for different years, months, days for both before and afternoon time and calculations for propagation of the long radio wave and its absorptions are all in agreement with data of observations. In addition, it is possible to calculate the distribution of electron density in the D-region from f_0E obtained by vertical soundings.