Abstract: Using the photochemical equilibrium daytime model,the electron density profiles in the 100-200 km region at low latitudes are calculated.The characteristics of the depth and width of E-F₁ valley are also analysed.The main results obtained are: (1) the variation of electron density with height and solar zenith angle depends on solar activity levels.It is found that the correlation of electron density with solar activity indices can be both positive or negative;(2) the solar activity can affect the morphology of E-F₁ valley.Under a certain solar activity level,the relation between the width and depth of valley and solar zenith angle can not be represented by a simple function at a given solar declination and geographical latitude;(3) the solar flare and geomagnetic activity influence obviously the distribution of the electron density;(4) O⁺(²P) and photoionization of nitre oxide may play a significant role in the 100-200 km height region.