Abstract: Well test results are very important foundation to draw up oil and gas field development scheme and choose and evaluate treating wells. But ambiguity of well test data restrained the accuracy and reliability of well test results so seriously as to lower their usefullness. Influences on well test results caused by well test design, data collection, model choosing (including wellbore, near wellbore effects, reservoir, outer boundary), and so on have been analyzed, and have been effectively determined.