In this talk, I will present our recent works for Dialog modeling and User simulation, and its application to DB-CALL (dialog-based computer assisted language learning) systems. The talk will be in two parts: 1) Our recent development of robust example-based dialog modeling technique and its application to DB-CALL with integration of error-feedback generation and translation/comprehension assistant. 2) More recent full fledged user simulation technique and it application to student grammar error simulation for DB-CALL. Our system will be ported into an intelligent service robot and will be deployed into Masan elementary school for practice this coming December.