A gas detection and purification device is provided for being carried by a user and includes a body, a purification module, a gas-guiding unit, and a gas detection module. The gas detection module detects a gas nearby the user to obtain a gas detection data, and the gas detection module controls the operation of the gas-guiding unit based on the gas detection data, guides the gas into the body, guides the gas to pass through the purification module for being filtered and purified to become a purified gas, and discharges the purified gas to a region nearby the user.