Low-hydrogen-containing polydimethylsiloxane (l-HPDMS) with different hydrogen contents and relative molecular mass was prepared via ring opening equilibrium polymerization, in the fixed-bed reactor which was filled with catalyst particles. The kinetics of D-4 ring opening reaction was studied to obtain the kinetic rate model. The physical model was determined by investigating the viscosity of the products at different aspect ratios and reaction temperature. According to the kinetic rate model and physical model, one-dimensional and pseudo-homogeneous ideal plug model was developed to simulate the fixed-bed reactor of l-HPDMS. The concentration of D-4 and relative molecular mass curves of products predicted by this model were compared to those experimentally measured in a bench-scale reactor. It can also calculate the bed height of reactor and provide the basis for the design of fixed-bed reactor, for the preparation of different l-HPDMS. Moreover, the effects of liquid hourly space velocity on the relative molecular mass were investigated.