In this paper, the research methods, experimental principles, fundamental theories, main findings, and implications for Young's modulus research of CNTs were reviewed and discoursed from both the ingeniously experimental measurements and distinctively theoretical calculations. The experimental measurements include the methods of vibration at CNT's free ends, and the CNTs bending or stretching with AFM tip(s). The continuum mechanical method, molecular-dynamics stimulation, and the mixture of both methods are involved in the theoretical calculations.