Installment payment is not only adopted by consumers but also by donators in nowadays. An installment donation allows donators to donate regularly over a longer period of time and pay smaller amounts for each donation. Although installment donation has facilitated many donation projects in practice, there are few relevant studies in the literature. The current study compares between installment donation and one-off donation. One preliminary experiment and four formal experiments were conducted to explore the influence of donation payment methods on people' willingness to donate, as well as its underlying mechanism and boundary conditions. The findings revealed that compared with one-off donation, installment donation can reduce perceived pain of payment and increase perceived donation effectiveness, thus enhancing people's willingness to donate. The above effect would not work for instant or urgent donation projects. Additionally, the installment payment method in donation could help elevate individual's general attitude towards charitable donations. This research enriches our understanding of the impacts of donation payment methods and provides valuable insights for encouraging donations.