Herein, a 1D numerical model was developed to simulate the enzymatic gelation of chitosan in thin film geometry, corresponding to a thin polymer solution cast onto a support. Mass and heat transfer phenomena were taken into account in the mathematical model and coupled to the chemical reactions involved during the chitosan gelation process (urea hydrolysis, equilibrium reactions, deprotonation of chitosan). External mass transfers involving water and ammonia evaporation as well as carbon dioxide intake and evaporation (depending on the gelation process stage) were integrated in the model. A comparison was done in deep cell geometry between the numerical results obtained with the 1D and a 0D model developed and validated in a previous work. The 1D model was then able to predict the influence of the external transfers on the chitosan gelation kinetics. More precisely the model developed herein exhibited that minimum initial concentrations of urease and urea are necessary to reach the advanced gelation pH during the process, which is a prerequisite for preparing thin chitosan membrane.