Abstract: This paper deals with the characteristics of rainwater chemical composition including continuous and intermittent rainwater, raindrop processes in Westerly-Wind Burst Event (WWBE) and in strong windstorm at the point of tropical west Pacific (4°S, 156°E) from Nov. 1992 to Feb. 1993. The results show that the pH value of pure "marine" rainwater is 5.55 and its Mn/Fe ratiois 0.54 at 4°S, 156°E. Cl- and SO42- are the mainions in rainwaters. The distribution of pH is the shape of "V" and Eh "∧". ∑S(-Ⅱ) has a decrese tendency with time and it tends to constant at last in continuous raindrop process. The pH and Eh have a increse tendency in intermittent raindrop process. The maximums of SO42-, NH4+, PO43- et al. occur after raindrop and maybe they are subproducts in raindrop process. The invese behaviour of NH4+, PO43-, et al. to the other ions demonstrate that the mechanism of NH4+, PO43-, SO42-, SiO32-, ∑S(-Ⅱ) produce and wash is different from the other ions in rainwaters. The concentrations of most components during WWBE are higher than those of raindro poccured before and after WWBE, but NH4+ is different. The concent rations of Cl- and SO42- in strong windstorm raindrop process are several times in normal raindrop, and the pH value has a distinct increse. This proved that seawater was carried by strong windstorm to air and droped with raindrop.