ATM is a computerized machine that provides bank customers to gain access to their accounts using magnetic encoded plastic card and code number. ATM is a real-time system that is very complex in design and application. The ATM provides 24*7 hours service, customer can withdraw cash up to certain limit with in a day any time. ATM is very beneficial for travellers, as they need not carry large amount of cash with them. The customer also withdraws brand new currency notes from ATM card. ATM also provides privacy to customer transactions. The Unified Modeling Language that is an object-oriented approach is used for modeling purposes know days by researchers and scientists. UML represents various static and dynamic views of system. The present paper represents class, sequence, activity and state model of ATM system. Valid and invalid Test cases are also designed for validation of models.