This research includes an idea that takes wide cares in modern applications through the object of Data Mining which is called Temporal Sequences. An investment of mathematical model known as Hidden Markov Model, of modeling Temporal Sequences. This research deals with an application combining between mathematics, computer and music. The problem of recognition of musical ladders is studied by using Hidden Markov Model, Some national songs are studied and modeled through this model. After making use of the computer for the songs under study, a result was reached to know a musical ladder which is used in national songs.