Abstract: It is very important for dynamic capacity-increase to work out the characteristic parameters of cable thermal circuit model accurately. Cable structure was introduced in detail and cable thermal model was elaborated. Principles of IEC method, shape factor method and thermal resistant correction method, which are main approaches to calculate the characteristic parameters, were set forth and features of the methods were investigated. Then we pointed out that shape factor method and thermal resistant correction method are useful and necessary complementarities to IEC method. Finally, we discussed the research trend to compute the characteristic parameters precisely.