Thermal problems due to the high current density of printed circuit boards (PCB)is one of the important problems that PI (power integrity) engineers focus on. With the rapid development of integration, the current density of PCB is sharp increases also, especially the power module with a large current is easy to happen overheating as the circuit board with high current density, and thus have a negative impact to the circuit performance. An accurate description of the relationship between the temperature rise and the current density of the complex PCB is an important problem that the PI engineer must properly solve. In this paper, we will firstly discuss how to accurately measure and evaluate the temperature rise caused by the current density on PCB，and then use it to guide the PCB design and find the current density and thermal problems existed in the PCB.