Computer Aided Engineering system for automotive piston design was developed which can predict total piston performance in a short time at the planning stage of piston design.Many previous studies attempted to calculate piston performance accurately with experimental data and their main purpose was not to create a tool for piston design. The purpose of this CAE system is to provide a tool for a designer to predict total piston performance easily and rapidly without experimental data. This system has following two characteristics.Firstly, new finite element methods were developed which can predict temperature distribution without experimental data, thermal skirt expansion for a strutted piston and skirt-to-bore contact pressure under engine operating conditions. The predicted result are accurate enough to predict piston performance at the planning stage of piston design.Secondly, the automatic mesh generating software was developed which creates three-dimensional piston modeling in less than 30 minutes. This software was developed so that a designer who has no experience of finite element analysis can operate easily and conversationally.