In recent years there has been an overwhelming demand for the development of the technology of autonomous rendezvous, in which the rapid and accurate onboard generation of rendezvous opportunities is a necessity, especially for the time-critical cases. A novel method, namely the two-dimensional rendezvous window method, is developed to determine all the opportunities of the autonomous rendezvous mission in this research. The concept of reachable domain (RD) of spacecraft and its computational method are firstly introduced. On this base, the method to determine all the time windows in the dimension of time-of-flight (TOF) for a fixed orbital wait time is proposed using the method to determine the RD and these time windows represent all the rendezvous opportunities for the given orbital wait time. And then, the two-dimensional rendezvous window method is proposed, which computes the time windows in both the orbital wait time and TOF dimensions to obtain all the mission opportunities. Numerical examples are provided to demonstrate the accuracy and rapidity of the method, which can achieve all the rendezvous opportunities within merely several seconds and thus is very suitable for the onboard mission planning of autonomous rendezvous.