Organizational capacity matters to the performance of aid agency in sustainable development. In recent years, development projects focus more on the capacity development of recipients, however, limited attention has been given to examine donor agency’s capacity. To address this issue, by integrating indicators involving the aid project management cycle, this study quantifies the capacity of donor agency (CDA) for member countries of Development Assistance Committee (DAC) in the Organization for Economic Co-operation and Development (OECD). After an overview analysis of aid agency capacity, we find that, France development agency, Finland international development cooperation agency, Belgium development agency and Luxembourg development agency rank ahead. The ranking results of overall-CDA and phase-CDA confirm the variances of CDA among OECD countries. Why? We apply general linear regression, two-stage least squares method and logistic regression analysis, based on climate aid projects, to explore what influences the overall capacity and phase capacity of aid agencies. It demonstrates that the funding amount of climate-related projects has a significantly positive effect on the capacity of aid agency, while controlling establishment time, administration costs and number of cooperative countries. This indicates that the climate investment encourages aid agency to improve capacity for sustainable development. Our work provides practical insights for strengthening the financial resilience of aid agency to tackle disproportional challenges posed by the COVID-19, to achieve Sustainable Development Goals.