With　the　increase　in　working　time,　the　geometric　errors　of　a　Horizontal　Machining　Center　(HMC)　will　also　increase　under　load,　temperature,　and　wear　conditions,　decreasing　the　machining　accuracy.　As　HMC　is　a　high-accuracy　machine　tool　with　a　high　nonlinear　system,　there　is　a　complex　coupling　relationship　between　errors.　Therefore,　how　to　thoroughly　evaluate　the　ability　of　a　machine　tool　to　maintain　its　machining　accuracy　with　the　extension　of　working　time　is　an　important　way　for　HMC　to　control　its　machining　quality.　In　this　paper,　this　ability　is　defined　as　machining　accuracy　reliability,　that　is,　under　specified　conditions,　the　machine　tool　can　work　normally　to　achieve　the　corresponding　machining　accuracy　ability.　To　solve　this　problem,　a　new　analysis　method　is　proposed　for　evaluating　machining　accuracy　reliability　based　on　the　nonlinear　correlation　between　errors.　The　nonlinear　relationship　between　machining　accuracy　and　errors　was　determined　using　multibody　modeling　technology.　The　effect　of　interaction　between　errors　on　machining　accuracy　reliability　was　analyzed　by　introducing　and　calculating　partial　correlation　coefficients.　Finally,　the　method　was　validated　using　a　four-axis　machine　tool.