Abstract: A new method called constant heat flux method was talked about the calculation of the heat transfer coefficient, h . The way of calculating h for the transient experiment was from step-change solution by giving a constant heat flux suddenly. If the time at which the changes colour of thermochromic liquid crystal(TLC) is known, then h can be found from the solution of so-called semi-infinite plate problem. Uncertainties of h calculated using the so-called two point method were discussed later. On the basis of this discussion it were found out how the accurate h could be got. The procedure of calculating h using constant heat flux method were listed and the free plant experiment are used to prove the method-s accuracy.