Abstract: Combining the characteristics of Markov theory and construction process of specialshaped arch bridge archrib，one Markov model for the accurate prediction of the spatial alignment of a specialshaped arch rib is established for the first time，and the calculation expression is derived of the spatial coordinates of the specialshaped arch ribs following the weakening of random error． Based on the above calculation expression，a spatial coordinate prediction method is proposed for specialshaped arch ribs，and the practicability of the method is verified by an experiment based on an engineering example． The calculation accuracy of the proposed method is compared with that of grey theory prediction method，Kalman filter method and least square method， the general development law of the spatial alignment is obtained of specialshaped arch bridge archrib． Numerical results thus indicate that the proposed method has perfect accuracy and reasonably high efficiency． 

Key words: Markov model, residual, specialshaped arch bridge, archrib, spatial alignment, accurate prediction