According to the agency, the university "enjoys an extraordinarily strong market position" and relies less than many other UK institutions on the government.
The rating has been carried out because the university has received internal approval to borrow up to £350 million, which would help fund a major building project in the north west of Cambridge.
"It is expected that any such borrowings would be applied towards further investment in research facilities, accommodation and other university assets," a statement from Moody's says.
John Nelson, managing director of higher education ratings at Moody's in the US, said he expected that governments in the US and UK would look to scale back public funding of universities over the coming years.
It was reassuring for investors that Cambridge had other, often global, sources of money, he explained.
Cambridge's global reputation meant that it could increase its intake of international students, giving it a "contingent" option to increase revenues, he said.
In addition, "they may want to really accelerate private philanthropy", he suggested.
Mr Nelson also pointed out that Cambridge had a major publishing and examination arm - a business model unlike any institution in the US.
Sarah Kieling, Moody's lead analyst for the university, said that the rating could be downgraded if Cambridge took on "more risky assets" or "if they were to choose to increase their borrowing".
The agency's statement also says that the decision to award the top rating "incorporates Moody's assessment of a strong regulatory framework for English universities through the regulator, the Higher Education Funding Council for England".
"Moody's notes that the University of Cambridge, which recently celebrated its 800th anniversary, enjoys an extraordinarily strong market position, as a global leader in education and research, supported by strong publishing and assessment businesses," the statement says.