A wearable blood pressure measuring device (2) includes a strap structure (21), a micro gas pump (22) and a pressure sensor (24). The strap structure (21) is adapted to be worn by a user and has an outer surface (210) and an inner surface (211). The micro gas pump (22) is disposed on the strap structure (21). The pressure sensor (24) is combined with the micro gas pump (22) through an elastic medium (23), disposed on the inner surface (211) of the strap structure (21) and in contact with skin (11c) of the user for monitoring blood pressure. The micro gas pump (22) is operated to drive gas, wherein the gas is transported into the elastic medium (23) to inflate the elastic medium (23) with the gas. The expanded elastic medium (23) pushes the pressure sensor (24) to press against the skin (11c) of the user for facilitating measurement of a blood pressure of a target artery (11b) by a flattening and scanning operation.