The inverse heat conduction problem based on surface temperature measurement is not only the key theoretical basis for the quantitative development of thermographic nondestructive techniques, but also an important and difficult issue. To identify the geometry of fixed-depth internal heat sources in a three-dimensional test-piece, the three-dimensional test-piece is simplified to a one-dimensional model so that establishing the relationship between the measured temperature and the internal heat sources in one-dimensional problem. The internal heat sources obtained can be corrected by the modified one-dimensional correction method until reaching the stopping criterions thus the result identified can make the error between the calculation temperature distribution and measured temperature distribution to be minimum. Numerical test cases show that the method is effective and simple.