Generally speaking, the major of applied mathematics is ok. You can try to take the postgraduate entrance examination and cross-disciplinary examination. Undergraduate students majoring in applied mathematics are very popular, and they can also engage in missile orbit calculation after graduation, which is needed in many aspects. The key majors of National Defense Science and Technology University mainly include physics, mechanics, mechanical engineering, optical engineering, instrument science and technology, material science and engineering, electronic science and technology, information and communication engineering, control science and engineering, computer science and technology, aerospace science and technology, and management science and engineering. Among them, mechanical engineering, optical engineering, communication engineering, control engineering, computer, aerospace, management science and engineering are national key projects.