Formative Evaluation is a method of evaluating a program while the program activities are forming or happening. Formative evaluation focuses on the "process" during which problems are timely spotted, corrected and adjustments made so that an intended goal can be accomplished. Through a four-month empirical research work with students of Grade 2010 of Continuous Education College of Dalian University of Technology as the subjects, the author in this article compares the teaching process and result of the experimental and the controlled groups, discusses the positive effects that formative evaluation gives to learning ESL by adult students while points out some of the problems that exist in this connection. The main purpose of this paper is to examine the degree of effectiveness of formative evaluation as applied in teaching adult students to learn English. The result of the author's research works reveals that the formative evaluation is effective in teaching adult students of English.