A numerical study has been conducted to analyze transient responding behaviors of fluid flow and heat transfer of the cryogenic methane at supercritical pressures, the physical phenomena closely related to the regenerative rocket engine cooling application. A steady-state cold flow is instantly enforced with a constant surface heat flux to activate the transient heat transfer process. The effects of surface heat flux, inlet flow velocity, and pressure on transient responses are studied in detail to obtain fundamental understanding of the underlying physical mechanisms. Results indicate that the increased fluid temperature during the heat transfer process leads to the significantly decreased fluid density at a supercritical pressure and consequently causes strong fluid thermal expansion, which results in flow oscillations. The strong pressure effect on thermophysical property variations in the supercritical-pressure heat transfer process, particularly in the trans-critical region, can lead to further extension of the transient responding process at a low inlet flow velocity and/or under a high surface heat flux. Flow oscillations become stronger and last longer under a higher surface heat flux and/or at a lower inlet flow velocity. An increased operating pressure slightly decreases the transient responding time. Under the tested conditions in the present work, the maximum transient response time is around 20 ms. (C) 2017 Elsevier Ltd. All rights reserved.