It has been known for a long time that hydrogen in the gas phase tends to inhibit gasification of char at low and intermediate temperatures. At higher temperatures, however, there are indications that hydrogen may speed up gasification. The mechanisms behind these effects are currently not understood. In this work, a newly developed detailed chemical kinetics model for char has been used to study the mechanisms behind the hydrogen inhibition and speed up of char gasification. For conditions assumed in this work, the hydrogen inhibition is found for T < 2000 K, while for T > 2000 K, hydrogen in the gas phase speeds up the char conversion. By studying the species reaction rates together with the individual rate of every heterogeneous reaction, the reasons for hydrogen influence on char gasification are attempted to be explained for a wide range of different temperatures in this paper. The focus is not on investigating a real gasifier but rather to understand the fundamental mechanism behind hydrogen inhibition of char.