Abstract: With the reference of the design specification of underground drainage system，the state transition matrix analysis method in the reliability theory is used to demonstrate that the limit on the number of pump spare in traditional reference specification is unreasonable.The relationship between the equipment and the reliability is pointed out under certain drainage ability.In view of the defects in previous drainage systems，different systems are classified to improve the integrity and accuracy of the reliability analysis.

Key words: Underground mine, Drainage System, Reliability, Availability