Abstract: A new developed device of drop-freezing experiment is described, the drops are cooled synchronously with surroundings, therefore, the temperature gradient of drops themselves is very small and the precision of experiments is improved. The cooling rate of the cold stage can be controlled and the freezing events are automatically recorded. The drop-freezing experiments have been carried out for several kinds of precipitation water which were sampled in Beijing from the end of 1995 to 1998. The freezing nucleus content calculated from spectra of freezing temperature of drops is given for each kind of precipitation, the differences among them are significant and the reasons are preliminarily discussed.