The invention relates to an unlocking key of a mechanical digital lock. The variable-code key with cylinder shifting teeth is characterized in that: a key rod is provided with multiple shifting tooth holes; the cylinder shifting teeth are mounted in partial or all shifting tooth holes, freely stretch/withdraw relative to the shifting tooth holes, and can switch in different shifting tooth holes; and only one cylinder shifting tooth can be mounted in the shifting tooth holes on the same circumference of the key rod. With a simple structure, the variable-code key provided by the invention not only realizes the intrinsic locking/unlocking function of a key, but also can change the combination of the cylinder shifting teeth and the shifting tooth holes on different positions of the key; and moreover, a novel key component integrating the encryption function and the key locking/unlocking function is created, two simple and convenient cylinder shifting tooth structures are provided, and more other cylinder shifting teeth with the same concept are also applicable. The variable-code key is simple to operate, convenient to use and high in security and suitable to be matched with the concealed digital locks of various safety boxes and security doors.