Abstract: The heat transfer for liquid metal through tube bundles is very important to fast reactors. Heat transfer for equilateral triangular bundles could be changed to heat transfer for annulus by using hexagonal heat transfer unit. After introducing hydraulic diameter correction and temperature correction for temperature difference and heat mixing, a new correlation for parallel flow of liquid metal through equilateral triangular bundles was derived. The new correlation matches with pre-existing experimental data well. It is also found that the second term of temperature correction can be used as a correlation for effective mixing length used in a subchannel approach.