This paper describes the dynamic modeling and simulation of spray tower saturator using one-dimensional flow control volume method, as a part of study for dynamic modeling of the humid air turbine cycle. The mass, energy and momentum exchanges between gas flow and water flow, as well as their conservations, are taken into consideration. Separate modules are built for gas flow and water flow, and are put into an application library of EASY5, which is general-purpose simulation software. Modular structure and mathematical causality needed by explicit modeling are maintained for the modules in the application library. Then spray tower saturators can be divided into arbitrary number of segments, and each one is modeled by a gas flow module and a water flow module. To exemplify the modeling method, two dynamic models with different number of segments are built for a spray tower saturator. For steady state analysis, quantity variations with tower height at design point are illustrated, and the results of the two models are compared. For dynamic analysis, two dynamic simulations are run to obtain response to 10% step increase of the gas and water inlet temperature respectively. Estimation of the dominant time constants by linearized model is also discussed.