The effects of longitudinal heat conduction on the performance of heat transfer surfaces are investigated by using a single-blow method. In the transient testing method for determining the heat transfer characteristics, exponential inlet temperature variations are made by using screen-mesh heater with small time constant and low frontal velocities of the test section, and the experimentally determined inlet temperature profile is used as the inlet fluid temperature condition. The effects of longitudinal heat conduction are negligible only if $gamma^act<0.05;and ;N_{tu}le3$ and should be considered if $N_{tu}le3$ The test results ate compared with the existing theoretical and experimental data and the validity of this technique is confirmed by the good agreement.