The aggregation of Perylene Diimide (PDI) and its derivatives strongly depends on the molecular structure, and therefore has great impact on the excited states. By regulating the molecular stacking such as monomer, dimer, J- and/or H-aggregate, the formation of different excited states is adjustable and controllable. In this study, we have synthesized two kinds of PDI derivatives - undecane-substituted PDI (PDI-1) and diisopropylphenyl-substituted PDI (PDI-2), and the films are fabricated with spin-coating method. By employing photoluminescence (PL), time-resolved photoluminescence (TRPL) and transient absorption (TA) spectroscopy, the excited-state dynamics of two PDI amorphous films have been investigated systematically. The result reveals that both films have formed excimer after photoexcitation mainly due to the stronger electronic coupling among molecule aggregate in the amorphous film. It should be noted that the excited state dynamics in PDI-2 shows a singlet fission like process, which is evidenced by the appearance of triplet state absorption. This study provides the dynamics of excited state in amorphous PDI films, and pave the way for better understanding and adjusting the excited state of amorphous films.