Weld joints of low carbon steel Q235 was prepared by rotary friction welding technique, and the effect of friction time and forge pressure on the seaming ratio and metallurgical quality of weld joints was investigated. The results show that the tensile strength of the seaming zones prepared by the rotary friction welding with different welding parameters is greater than or equal to that of the base metal, in other word, the variation of welding parameters will simply affect the seaming ratio (the ratio of the length of seamed portion to the total length of a joint), while the quality of joints is direct determined by the seaming ratio. Further study shows that the seaming ratio increases with the forging pressure, but the increment slows down gradually and eventually reaches 100% when the forging pressure reaches a critical value. The axial shortening amount increases along with friction time, which then decreases the seaming ratio. The width of the weld zone becomes larger and the grain size increases with friction time. The grain size is not uniform near the weld seam with streamline structure presented. It is concluded that large forging pressure and short friction time are helpful to improve the seaming ratio, reduce the grain size and enhance the quality of the joints.