Abstract: The experimental technology using X-ray free electron laser source (XFEL) has irreplaceable advantages in the research direction of microstructure and electronic structure in the fields of chemistry, biology, materials and other fields. Free electron laser (FEL) sources can emit ultrashort X-ray pulses with pulse durations of 10 fs, making conventional optical lasers ideal for pump-probe experiments. One of its most important applications is the study of ultrafast dynamics inside microstructures (femtosecond pumpprobe measurement). It is a typical technology for studying ultrafast dynamics at very small scales. The rapid developmenting ultrafast X-ray spectroscopy experimental technology has been widely used in different research fields. This article mainly introduces the application and technological development of femtosecond X-ray free electron lasers in the field of photochemistry in recent years. In the future, with the completion of the hard X-ray free electron laser in Shanghai, it can support multi-disciplinary and interdisciplinary fields such as physics, chemistry, energy, materials, environment, etc., and make significant scientific research achievements.