The expert witness is indispensable in a medical malpractice case. However, there are three main defects in the currently existing expert witness system. One is incompetence of expert witnesses. Another is professional negligence of expert witnesses. The other is dishonesty of expert witnesses. To make the expert witness system more efficient, this article examines currently existing rules and offers some proposals regarding the three issues. For the first one, the suggestion of this article is to rely on the standards of expert qualification and admitting expert testimony. For the second one, this article distinguishes expert witnesses from lay witnesses, and concludes witness immunity should not be extended to a friendly expert witness. Thus negligent experts should be regulated by professional responsibility. For the third one, the bias of experts is inherent in the adversarial system. This article gives some proposals to control it, but it is almost impossible to get rid of it.