Formaldehyde, as one of the simplest reactive carbonyl species(RCS), is regarded as a potential carcinogen and a sick house syndrome gas. Recent studies have shown that abnormally high levels of formaldehyde may result in cognitive decline and spatial memory deficits, asthmatic symptoms,Alzheimer’s disease, and cancer. Due to the harmfulness of high levels of formaldehyde in nature and humans, it is of great significance to further elucidate the roles and functions of formaldehyde by a noninvasive detection approach. Fluorescence imaging has become a powerful and popular tool in monitoring bio-species owing to their high sensitivity and selectivity, excellent spatiotemporal resolution and non-invasion nature. Therefore, fluorescent probes are widely applied to track and detect formaldehyde in vitro and in vivo which have attracted more and more interest recently. This review focuses on various strategies to design the fluorescent probes for detecting formaldehyde based on different recognition groups. Formaldehyde, as one of the simplest reactive carbonyl species (RCS), is considered as a potential carcinogen and a sick house syndrome gas. Recent studies have shown that abnormally high levels of formaldehyde may result in cognitive decline and spatial memory deficits, asthmatic symptoms, Alzheimer’s disease, and cancer. Due to the harmfulness of high levels of formaldehyde in nature and humans, it is of great significance to further elucidate the roles and functions of formaldehyde by a noninvasive detection approach. Fluorescence imaging has become a powerful and popular tool in Monitoring bio-species due to their high sensitivity and selectivity, excellent spatiotemporal resolution and non-invasion nature. Therefore, fluorescent probes are widely applied to track and detect formaldehyde in vitro and in vivo which have attracted more and more interest recently. on various strategies to design the fluorescent probes for detecting formaldehyde based on different rec ognition groups.