The main goal of this paper is to present the design of an MzScheme program that allows us to simulate the behavior of transition P systems. For that, a library of procedures have been developed that work in two stages. In the first one, the parsing/compiling stage, the input P system is checked, and if it is well defined, then it is represented by means of an internal grammar. In a second stage, the simulation, the computation tree associated to the P system is generated until a prefixed level.