5%, 10%, 15%, 20% and 25% PEG-6000 solutions were used to simulate drought stress conditions for the germination of Galinsoga parviflora. Germination time, germination percentage, daily relative germination rate, germination potential, germination index and vigor index under each water stress were recorded. The effects of drought stress through PEG treatment on seed germination, and the germination recovery under optimal conditions after presoaking with PEG solution were studied in a series of laboratory tests. The results showed that as the water stress was aggravated, the seed germination and seedling growth were more seriously inhibited, and daily relative germination rate, germination percentage, germination potential, germination index, vigor index, and the length of seedlings and roots were decreased, and germination time was extended longer. When the PEG concentration was 20% or 25%, the seeds of G. parviflora did not germinate. The linear regression equation of seed germination under water stress predicted that the critical value of PEG concentration (drought tolerance) was 12.9%. The seeds recovered their germination under optimal conditions after presoaking with 20% or 25% PEG solution. Nevertheless, when the presoaking time was same, 20% PEG solution had little effects on the seed germination of G. parviflora, showing a strong recovery, while 25% PEG solution had adverse effects on the seed germination of G. parviflora, showing a weak recovery.