Abstract: Polar Mesosphere Summer Echoes (PMSE) are very strong radar echoes from altitudes near the polar summer mesopause. ECT-02 is carried out when PMSE in polar mesopause was occured. Based on the experiment results of ECT-02, the electron number densities and dust charge number densities are deduced in the paper. The data will provide a good basis to study various features of PMSE. By analyzing the data, one can find that dusty plasma in polar summer mesopause is weakly ionized and weakly coupled. The variable disturbance of electron density is used to explain the generation mechanism of PMSE. The stronger disturbance of the electron density corresponds to the stronger radar echoes, and when the disturbance becomes small, the radar echoes become weak, even disappear.