The present invention discloses a robot joint structure that includes a servo and a connection part. The servo includes a servo main body and an output shaft, and one end of the output protruding out of the servo main body. The servo main body includes a servo plate at one side surface thereof. The servo plate is fixed to the output shaft and capable of rotating together with the output shaft. The connection part includes a first connection arm, and the first connection arm defines at least one connection chamber allowing the servo plate to be inserted therein and mating with the servo plate, to fix the connection part to the servo plate. The servo and the connection part of the robot joint structure mate with each other, which avoids the disengagement during rotation. The assembling process is simple, which enhances the user experience.