Traditional theory of ecological carrying capacity, which was established on the basis of quantitative dynamic of natural biological population, met extreme challenge while applied to human ecosystem research. This paper summarized the key problems and dilemmas in three aspects of theoretical foundation, regulation mechanism and estimation method of human carrying capacity research, respectively. As to theoretical foundation, the objectivity of human carrying capacity has always been the arguing issue among ecologists and economists. As to regulation mechanism, current achievements of carrying capacity researches have been unable to explain the unusual mechanism that the development of economy and society didn′t grow along Logistic increasing law. Furthermore, current estimation methods could not provide practical decision-making foundation for the development of economy and society either. With extensively reviews on the latest achievements in ecological science, earth science, physics and environmental archaeology, this paper summarized that complexity of earth ecosystem and social property of human carrying capacity as well as researchers′ wrong perception on carrying capacity were three main reasons that led to the research dilemma of human carrying capacity. Based on this understanding, the future ways out from the dilemma and the key fields of human carrying capacity research are proposed at the end of the article.