Abstract: The note for the observations of the microphysical structure of fog by optical-electrical method and some problems about the data processing are described in the Paper.Analysis of microphysical properties of fog,such as the drop concentration,the size distribution of the fog drops and the water content in the fog,is given.The result shows that distribution of drop spectrum is the most important characteristic factor in the fog evolution process.Basic characters for fog development are: 1)the number of larger drops increases,2)the fraction of smaller drops decreases and 3)the drop size distribution widens.