In view of the key engineering and technical issues in the development of cislunar space, studies are carried out from the perspectives of cislunar space transportation, resources of the Moon and small celestial bodies, lunar robots, and the cislunar space economic system. Cislunar space transportation can be divided into phases such as round-trip between the Earth and the orbit, Earth-Moon transfer, and lunar landing and ascent. It is necessary to develop different vehicles, transportation modes and reuse schemes according to the environmental characteristics of different phases, and consider the integrated design of the space station near the Earth and manned lunar exploration. The abundant resources of the Moon and small near-Earth objects are the material basis for the development of cislunar space. The geostationary orbit is an ideal industrial park in cislunar space. The vacuum, low gravity, low temperature and sufficient solar energy in lunar space facilitate the development of electrification transportation such as magnetic levitation, space elevator and skyhook. Facing the harsh lunar environment and scarce human resources, the lunar robot will play a leading and main role in infrastructure construction, astronaut accompaniment and assistance, human-machine cooperation. The development of cislunar space is not only for manned landing on the Moon, but also for the establishment of cislunar economic system. It will promote the national interests to extend from the land and the sea to cislunar space, promote the development of space industry from the earth to cislunar space, and accelerate the progress of human society from the earth civilization to the solar system civilization.