The spatial photosynthetic heterogeneity within leaves is an important prerequisite for the studies on the photosynthetic model, the mechanism(s) of photoinhibition and light protection, etc. However, currently the in vivo measurement of the spatial photosynthetic heterogeneity within leaves is difficult. The present study improved the device assembled by Vogelmann & Evans (2002), thereby acquired the photosystem II (PSII) maximum photochemical efficiency (Fv/Fm) images within leaves. Finally, these images were processed and data of Fv/Fm and its spatial variations could be obtained, with the aid of MATLAB software. Based on the innovative technique, an investigation of the effects of strong light on the Fv/Fm and its spatial heterogeneity within leaves has been carried out. It was found that Fv/Fm within leaves was not homogonous. Strong light led to a general decrease of Fv/Fm (PSII photoinhibition) across leaf section, and the palisade tissue close to the epidermis layer had high tolerance to photoinhibition. Compared with control, short-term photoinhibition caused a larger spatial variation of Fv/Fm within leaves, which may be related to the chloroplast-avoidance response induced by high-fluence. On the contrary, long-term light inhibition led to a smaller spatial variation of Fv/Fm within leaves, indicating such mechanism is no longer effective. Compared to other types of chlorophyll fluoremeter, the device in the present study can in vivo obtain the panoramic picture of Fv/Fm within leaves, providing a powerful tool for the studies on the mechanism(s) attributed to the spatial heterogeneity of photosynthetic capacity of leaf, which is critical for the understanding on several hot spots in the research field of photosynthesis.