A wearable device, comprising: a motion sensor configured to detect whether a user is in a motion state; a heart rhythm sensor configured to detect the user's signal of heartbeat interval; a memory storing algorithm program and database configured for data processing, comparison and analysis; a microprocessor configured to calculate, filter and judge the signal of heartbeat interval and a feedback module configured to display or alarm a judgment result, wherein the wearable device is configured to detect the user's motion state and heartbeat condition, and to detect heart rhythm when the user is not in the motion state to judge whether there is atrial fibrillation; characterised in that the detection of the user's motion state and heart beat condition is continuous, and in that the microprocessor is configured to calculate, filter and judge the signal of heartbeat interval by: calculating heartbeat counts in a preset time period in which the preset time period is appropriated and fixed; calculating the average of all heartbeat intervals, standard deviation, and time differences between the two consecutive heartbeat intervals in the preset time period; comparing the signal of heartbeat interval with a first normal filtration database to judge whether there is non-atrial fibrillation; excluding abnormal heartbeats from the signal of heartbeat interval to produce an uncertain heartbeat signal; counting heartbeats in the uncertain heartbeat signal; comparing the heartbeats in the uncertain heartbeat signal with a second normal filtration database to judge whether there is atrial fibrillation; if a number of heartbeats counts in the uncertain heartbeat signal is greater than a predetermined threshold, calculating a heartbeat variation degree of the uncertain heartbeat signal; and comparing the heartbeat variation degree with a second abnormal filtration database to judge whether there is atrial fibrillation. a motion sensor configured to detect whether a user is in a motion state; a heart rhythm sensor configured to detect the user's signal of heartbeat interval; a memory storing algorithm program and database configured for data processing, comparison and analysis; a microprocessor configured to calculate, filter and judge the signal of heartbeat interval and a feedback module configured to display or alarm a judgment result, wherein the wearable device is configured to detect the user's motion state and heartbeat condition, and to detect heart rhythm when the user is not in the motion state to judge whether there is atrial fibrillation; characterised in that the detection of the user's motion state and heart beat condition is continuous, and in that the microprocessor is configured to calculate, filter and judge the signal of heartbeat interval by: calculating heartbeat counts in a preset time period in which the preset time period is appropriated and fixed; calculating the average of all heartbeat intervals, standard deviation, and time differences between the two consecutive heartbeat intervals in the preset time period; comparing the signal of heartbeat interval with a first normal filtration database to judge whether there is non-atrial fibrillation; excluding abnormal heartbeats from the signal of heartbeat interval to produce an uncertain heartbeat signal; counting heartbeats in the uncertain heartbeat signal; comparing the heartbeats in the uncertain heartbeat signal with a second normal filtration database to judge whether there is atrial fibrillation; if a number of heartbeats counts in the uncertain heartbeat signal is greater than a predetermined threshold, calculating a heartbeat variation degree of the uncertain heartbeat signal; and comparing the heartbeat variation degree with a second abnormal filtration database to judge whether there is atrial fibrillation. calculating heartbeat counts in a preset time period in which the preset time period is appropriated and fixed; calculating the average of all heartbeat intervals, standard deviation, and time differences between the two consecutive heartbeat intervals in the preset time period; comparing the signal of heartbeat interval with a first normal filtration database to judge whether there is non-atrial fibrillation; excluding abnormal heartbeats from the signal of heartbeat interval to produce an uncertain heartbeat signal; counting heartbeats in the uncertain heartbeat signal; comparing the heartbeats in the uncertain heartbeat signal with a second normal filtration database to judge whether there is atrial fibrillation; if a number of heartbeats counts in the uncertain heartbeat signal is greater than a predetermined threshold, calculating a heartbeat variation degree of the uncertain heartbeat signal; and comparing the heartbeat variation degree with a second abnormal filtration database to judge whether there is atrial fibrillation.