The forming behaviors of tailor-welded blanks (TWBs) have been widely studied since they were first developed as a way of using collectible offal. A typical TWB is composed of several base metals, which might have different mechanical properties as well as thickness. Moreover, a TWB contains heat-affected zone (HAZ) which has quite different mechanical properties as base materials do. Little published information on HAZ is available up to now, especially its numerical modeling. It is not clear how much HAZ affects the formability and the springback of TWB. In this paper, the mechanical properties of HAZ are determined from hardness test and tensile test. The eccentric load applied in tensile test is essential for decomposing the properties of the base materials and the HAZ. Various finite element modes for TWB are presented. An appropriate model based on the considerations of accuracy and computing efficiency is suggested. Free bend test (three-point bend test) and stretch bend test (OSU formability test) are performed to verify the proposed numerical modeling technique for TWBs.