The invention discloses a prediction method for fatigue reliability of a cable support in a subway tunnel. The method comprises: considering nondeterminacy of model parameters, using a response surface method to generate parameter samples; according to the parameter samples, establishing a finite element model, converting a track irregular spectrum to an irregular spatial waveform, used to adjust node coordinates of steel rail nodes in the model; the steel rail node being provided with a vertical pressed non-pulled unit, used to simulate wheel-rail contact; establishing a train-rail model, a tunnel-soil mass model, and a support-cable model and solving, to obtain stress time-history of the node on the root of the support, amplitude of the node being maximum; using a rain-flow counting method to calculate fatigue life; according to the parameter samples and a fatigue life value to fit the response surface and calculating a reliability index; accordingly, a series of fatigue life target values can be assigned, calculating the corresponding reliability index, so as to draw an invalid exceedance probability curve of the support.