We present a computational study employing Object Kinetic Monte Carlo simulations to investigate the behavior of D in self-irradiated Mo samples. Our simulations reveal that vacancy clusters contributing significantly to D diffusion, trapping, and desorption behavior. It is found that vacancy clusters play an important role in slowing the diffusion of D within the irradiated materials, which can be represented by an effective trapping energy that associated with mobile D atom interacting with the multiple types of vacancy clusters. Furthermore, we analyze the thermal desorption spectrum of D from irradiated Mo samples, demonstrating a saturation effect in D retention at higher damage levels. Notably, the presence of vacancy clusters significantly influences the thermal desorption spectrum and leads to the observation of negative desorption rates at specific temperatures. We also investigate the D desorption behavior under constant temperature storage conditions, revealing a non-exponential desorption rate with a 1/t decrease over time. Our study sheds light on the complex interplay between D and vacancies/vacancy clusters in irradiated materials, highlighting the importance of considering vacancy clusters in modeling D retention and desorption processes.