In this paper, three different growth mechanisms of photovoltaic material CZTSe based on CZTSe phase diagram were analyzed in details: (1) growth pathway based on zinc-rich phase, (2) growth pathway based on Cu2SnSe3-ZnSe reaction and (3) growth pathway based on Cu-rich phase. Then, the optimal reaction pathway was summarized for the growth of CZTSe films. The “4-chamber-8-source co-evaporated system” which was developed by SIAT was introduced to deposit the CZTSe films in this paper, and the system monitored the phase change during the growth of CZTSe successfully and different phase change processes corresponded with different temperature change pattern. These conclusions would be a significant guidance in future work.