  In this paper, the theoretical aspects behind longitudinal RF capture are
reviewed and the capture process is simulated via a program based on this
theory. Four kinds of cases with different initial distribution and capture
curve are considered, i.e. uniform distribution with adiabatic capture, uniform
distribution with non-adiabatic capture, Gaussian distribution with adiabatic
capture and Gaussian distribution with non-adiabatic capture. The simulation
results are compared each other and discussed, and Gaussian distribution with
adiabatic capture is demonstrated having a higher capture efficiency and
leading to a shorter bunch length. In addition, the BPM induced signal is
simulated with high input impendence, i.e. $1M\Omega$, and low input
impendence, i.e. $50\Omega$, respectively. Finally, the BPM signal of Heavy Ion
Medical Machine (HIMM) is estimated and compared with measured one, and a good
agreement is achieved.
