Abstract: Aiming at the rotation joints in deployment mechanism of umbrella antenna used in a certain satellite, the movement reliability has two parallel performance functions： the performance function according to rotation work and that according to rotation moment. Corresponding to the beginning phase, outspreading phase and the phase that the net has pressing force, the expressions of two performance functions were established respectively according to the position relations of all components. Secondly, two-kind reliabilities can be calculated from the two performance functions by means of the random functional moment method and the second moment method for reliability analysis. The movement reliability of one rotation joint can be got from two parallel reliability models. Finally, the change curve of the movement reliability of umbrella antenna outspread mechanism with outspreading angle was analyzed with an example. To the whole outspreading course, the reliability has the trent of first increase and then decrease, and the reliability of the beginning phase was smallest.