Aiming at the 110 m fully-steerable radio telescope(which is called QTT for short ) to be built in the future, in order to improve the main reflector precision, the traditional structural concepts were analyzed based on the best fit paraboloid. It is the uneven deformation of the reflector that results in the lower precision. It is mainly due to the following three aspects: the concentrated loads exist on the main reflecting surface, the back frame supporting system is unreasonable and the back frame structure has a poor performance. Based on this, the catching points of the secondary reflector supporting legs were changed, the space truss structure combining cones and quadrangular pyramids were adopted as the back frame structure design, and a kind of polar symmetry umbrella structure was proposed as the supporting system for the back frame structure. Finally the introduced scheme for the fully-steerable radio telescope significantly improved the main reflector precision, its maximal RMS was reduced to 0.306 mm. Compared with the fully-steerable radio telescope GBT which has the largest diameter in the world, the reflective surface area of QTT increases 10%, the surface precision improves 12.6% and the total weight decreases 40%. The QTT performance reaches the international advanced level.