The steady-state and transient behaviors of a high-pressure ethylene polymerization reactor have been analyzed for a continuous stirred autoclave reactor consisting of two reaction compartments. The nonlinear temperature dependence of the specific initiator consumption rate is modeled using the initiator efficiency factor which varies with reaction temperature. It is shown that there exists a critical reaction temperature at which the steady-state process gain (reactor temperature change/initiator feed rate change) changes its sign. When only the first reaction zone temperature is controlled by regulating the initiator injection rate, the second zone temperature is strongly affected by the first zone temperature for certain initiator types. It has also been shown that the volume ratio of the two reaction zones is an important reactor design parameter that affects the temperature rise in the second reaction zone. Dynamic closed loop reactor simulations have also been carried out to illustrate potential control problems when the reactor operating condition is changed from one steady state to another.