The ultra-weak luminescence (UWL) feature of plant seeds is investigated. Before UWL measurement, the maize seeds are moistened in distilled water for various periods, which are 2h, 4h, 6h and 8h. And then the seeds are dried to the mass they had before moistened. The UWL measurements are made before and after distilled water injects into measured samples. A kind of double exponential function is proved fitting the tested data well as the coefficient of determination of fitting is above 0.97. It is observed that UWL properties of different samples have obvious regularities. The dry seeds contain a large number of hydrophilic pores, so water quickly permeates into maize seeds and forces the seeds to produce stress UWL after water injection. The intensity of UWL depends on the structure of seeds and the time of moistening. Over a period of time, the different UWL intensity of samples decays to the same level as the seeds without moistening. The study results contribute to the understanding of relationships between the structure of seeds and metabolic activity and its UWL specialties. The paper provides a new idea for nondestructive testing of plant seeds.