Knowledge can be divided into technical knowledge on nature and institutional knowledge on human itself. The mainstream economic growth theory highlights the effect of technical knowledge on economic growth but overlooks the effect of institutional knowledge on economic growth. The institutional knowledge distribution status determines the effect of the possibility and sufficiency on economic growth. Therefore, all knowledge should be included in economic growth analysis framework. The application of knowledge to economic growth is really the result of human capital optimization because human capital not only embodies technical knowledge but also reflects institutional knowledge, i.e., the second feature of human capital. The basic path for the economic development is making efforts to raise human capital, especially to promote institutional knowledge level.