A theoretical analysis is carried out to study the performance of a plug flow reactor producing low density polyethylene under the high pressure condition. The model takes the pseudo-steady state assumption for the free radicals. Under various operating conditions the reactor temperature, the initiator and monomer conversions, and the number average molecular weight are investigated by the method of numerical analysis. This provides useful information for the operation and control of high pressure polyethylene tubular reactors. The reactor performance appears to be the most significantly affected by the heat transfer coefficient and becomes more sensitive to changes in various parameters as the heat transfer coefficient takes lower values. The reactor length required becomes shorter as the heat transfer coefficient takes higher values. It is noticed that the reactor performance is very sensitive to changes in the heat transfer coefficient, the jacket temperature, and the feed initiator concentration and less sensitive to changes in the feed temperature. The number average molecular weight of polyethylene prduced is also examined under various operating conditions. It turns out that the molecular weight is closely related to the monomer conversion.