A key scanning method, a scan method for a key scan circuit, and an input device thereof are provided. The key scanning method comprises performing a first scan procedure which includes triggering a first main scan line and reading electrical signals received via a plurality of signal sensing lines to determine whether any of the keys among a first key group is triggered. Then, performing a second scan procedure which includes triggering at least one of a plurality of secondary scan lines and reading the electrical signals received via the plurality of signal sensing lines to determine whether any of the keys among a second key group is triggered. In the key scanning method, the first scan procedure and the second scan procedure are performed one after another, and each of the secondary scan lines is triggered at least once.