The transverse emittance at the exit of the China Spallation Neutron Source（CSNS）DTL is measured regularly every year. However, recently, the measured transverse emittance growth became larger than the his-torical data. It is also bigger than the simulated emittance. The process of measurement, data analysis and matching methods used are almost the same. Several factors con-tributed to the transverse emittance growth are analysed and presented in this paper. Compared to other factors, longitudinal mismatch contributes the most growth.