Pulsating flows in a Helmholtz pulse combustor tailpipe have been numerically studied with a CFD simulation method. When a pulsating jet from a pulse combustor tailpipe is used for impingement heat transfer, temperature around the tailpipe exit depends on the impingement geometry, i.e., a confined or unconfined impingement zone. The objective of this work is to study the effects of ambient temperature on pulsating tailpipe flow characteristics. Two cases with different levels of ambient temperature were simulated. The case with higher temperature was validated with available experimental data in the literature. Simulation results showed that, based on equivalent mean mass flow rates, the case with cooler ambient air had, compared to the other case, greater mean inlet pressure, lower amplitudes velocity oscillation along the tailpipe, and greater mass flux oscillation amplitudes near the tailpipe exit. However, although the mean temperatures at the tailpipe exit were significantly different between two cases, mean velocities along the tailpipe were still the same. The linear acoustic theory was applied to compare with the CFD simulation. With appropriate assumptions, the solution was a reasonable approximation of the velocity amplitude profile.