Abstract: In 1963, Dr. Qian Xuesen (Tsien Hsue-Shen) pointed out the significance of the study on interplanetary travel, and revealed the potential utilization of electric propulsion in his book ``Introduction to Interplanetary Travel''(in Chinese). Compared to traditional chemical propulsion, the high-specific-impulse electric propulsion is promising to carry more payloads and achieve enhanced flight performance for interplanetary travel. Meanwhile, the design and optimization of continuous-thrust transfer trajectories resulting from the use of electric propulsion have brought new research contents to the traditional spacecraft's orbital dynamics, and meanwhile guides the future development of electric propulsion. This article will present technological progress of electric propulsion, continuous-thrust trajectory design, and comprehensive optimization of interplanetary flight, attempting to describe the fundamental content and approach of the utilization of electric propulsion for interplanetary travel, as well as for manned deep-space flight.