Do you want impose a heat flux function of position? if yes, this is made  through a User Defined Function - UDF written in C. IIt is not a big issue. here you ca find some examples

http://cdlab2.fluid.tuwien.ac.at/LEHRE/TURB/Fluent.Inc/fluent6.2/help/html/udf/node77.htm

and some procedures to help you

http://www.cfd-online.com/Wiki/Fluent_FAQ#User-Defined_Function_.28UDF.29_Related

Thank you very much  it's very helpful 

Actually I need to represent the heat flux along the weld as a function of coordinate and time using ANSYS transient solution.The problem is how to make heat flux move along the welding line.

You will need only change your functions inside the UDF. eg.

xref = xo + v*time

heat = a+ b(x+xref)

Something like that, or parametric equations with time as independent variable. 

The details can be more hard to coding, but the  idea is that.