Abstract: SU-8 thick resist lithography has become the mainstream technology for structures with high aspect ratio in the micro-electro-mechanical system (MEMS) and integrated circuits (ICs). So as to replace expensive and time-consuming lithographic experiments, lithography simulation becomes an increasingly valuable tool for predicting results and optimizing manufacture process. A three-dimensional (3D) lithography simulation model is developed for the ultraviolet (UV) process of SU-8 resist. The model utilizes waveguide (WG) method based on rigorous electromagnetic field theory, which is more comprehensive than its two-dimension counterparts. Using this model, the light intensity distribution and morphology of photoresist after development process can be stereoscopically predicted. A series of simulations and experiments have been conducted to verify the validity of the model. The study is carried out on SU-8 under UV source with 365 nm and 2.6 mW/cm2. Simulation results are given by cross section image and stereogram combined with corresponding experimental outcome. The results confirm the validity of the simulation model and prove that the 3D hybrid model is faster than other methods and remains accurate.