A finished drug product weighing device (20) used for a dispensing device (1), the finished drug product weighing device comprising a finished drug product conveying module (21) and a weighing module (22), the finished drug product conveying module (21) is used for acquiring a finished drug product after dispensing by means of the dispensing device (1) and conveying the finished drug product to the weighing module (22); and the weighing module (22) is used for detecting the weight of the finished drug product and feeding the detection result to the dispensing device (1). After the existing dispensing device (1) completes dispensing, the weighing module (22) checks the weight of the finished drug product and sends the checking result to the dispensing device (1), and the dispensing device (1) can thus perform further correction according to the weighing result, improving the weighing and checking efficiency of the existing dispensing device (1), reducing the finished drug product loss rate, improving the dispensing safety of the dispensing device (1). A finished drug product weighing method based on the finished drug product weighing device (20). A dispensing device (1) comprising the finished drug product weighing device (20).