The frequency unstability, voltage unstability and chain reactions could occur on renewable energy transmitted by ultra high voltage direct current(UHVDC) lines.Therefore, the theory, application and cases of power transmission technologies which are commonly researched and could be utilized in planning in China are analyzed.From the angle of alternative technology, the traits of half-wave-length transmission that act as a substitution of UHVDC transmission and can construct three-dimensional grid are put forward.Flexible DC transmission has preponderances such as practicability to organize DC network, which can be utilized in the scenes to admit renewable energy and establish DC network.The economy of two alternative technologies is compared based on the principle of annual fee per unit capacity.Conclusion is that flexible DC transmission costs less.Moreover, the choice of DC voltage level on the basis of least annual fees under diversified combinations of transmission distance and capacity is researched and analyzed.The characteristics of frequency modulation of virtual synchronous machine for new energy are analyzed as an assistive technology.Its application in new energy high permeability sending or receiving end power grid is presented.The dynamic reactive modification capacity of synchronous condenser is analyzed.Its application in transmission systems of new energy is presented.On the basis of trajectory of four alternative and assistive technologies and the variation of the pattern of power system in the history and anticipated, the tendency of technology development and influence on the shape of power system are discussed and forecasted.