The invention discloses a machining center knife magazine manipulator reliability testing method based on an onsite load characteristic. The method comprises the three steps of onsite data acquisition, a data processing process and laboratory reliability testing. The data processing process comprises the following six steps of calculation of average knife switching frequency alpha of a knife magazine manipulator and an average fault interval knife switching frequency MTBFn in an actual condition, establishment of a statistical distribution model of a cutterhead/cutter chamber insertion total weight Mi, determination of an average knife insertion number V(Zj) during each weight grade reliability test of a cutterhead/cutter chamber, establishment of a knife insertion distribution model of the cutterhead/cutter chamber at each weight grade, calculation of parameters of counterweight blocks selected for the tests and calculation of the knife switching frequency of each counterweight block during the tests. Through performing a laboratory reliability test on the machining center knife magazine manipulator by use of the method, the method can effectively shorten the assessment period of the knife magazine manipulator and improve the assessment precision.