Cannabidiol (CBD) is an abundant non-psychoactive phytocannabinoid in Cannabis extracts. Mechanic studies have indicated that CBD has high affinity on a series of receptors, including type 1 cannabinoid receptor (CB1), type 2 cannabinoid receptor (CB2), GPR55, transient receptor potential vanilloid (TRPV), peroxisome proliferator-activated receptor gamma (PPARγ). By modulating the activities of these receptor, CBD exhibits multiple therapeutic effects, including neuroprotective, antiepileptic, anxiolytic, antipsychotic, anti-inflammatory, analgesic and anti-cancer properties. Recently, according to some initial studies, CBD’s anti-inflammatory properties could be applied for treat or prevent COVID-19. CBD has gained increased attention in recent years because of its great potential to treat various human diseases. This review provides a current overview of CBD’s applications in human diseases, from mechanism of action to clinical trials.