FLAC 3D（Fast Lagrangian Analysis of Continua）由美国ITASCA公司开发的仿真计算软件。目前，FLAC有二维和三维计算程序两个版本，二维计算程序V3.0以前的为DOS版本，V2.5版本仅仅能够使用计算机的基本内存（64K），所以，程序求解的最大结点数仅限于2000个以内。1995年，FLAC 2D已升级为V3.3的版本，其程序能够使用扩展内存。因此，大大扩展了计算规模。FLAC 3D是一个三维有限差分程序，目前已发展到V6.0版本。(FLAC 3D (Fast Lagrangian analysis of continuum) is a simulation software developed by Itasca company. At present, FLAC has two versions of two-dimensional and three-dimensional calculation program. The two-dimensional calculation program before V3.0 is DOS version, and the v2.5 version can only use the basic memory of the computer (64K), so the maximum number of nodes of the program is limited to less than 2000. In 1995, FLAC 2D was upgraded to v3.3, and its program can use extended memory. Therefore, the computing scale is greatly expanded. FLAC 3D is a three-dimensional finite difference program, which has been developed to version 6.0.)