The invention discloses a method for detecting a leakage passage position of a dam by using a cold source method. The method comprises the steps of measuring temperature data of each drilled hole along the hole depth of a target region of a dam region in an initial state; uniformly putting an equal amount of frozen brine at the position corresponding to each depth in each drilled hole by using an injector; after standing for 5 min, periodically measuring the temperature value of each drilled hole along the hole depth; drawing an isothermal diagram of each depth of the target region according to the measured temperature data of the drilled hole, wherein the region with abnormal temperature, which is a low-temperature region, is a possible leakage passage position; and meanwhile, drawing a curve graph for the variation of the temperature values of underground water of each drilled hole at different moments with depth, wherein the amplitude of variation of the temperature value corresponding to a certain depth is the maximum, the position corresponding to the temperature value is the possible leakage passage position, and thereby the leakage passage position is comprehensively judged. The detection method has the advantages of easiness in operation, high efficiency, low detection cost, integration of two leakage passage position judgment methods, reliable detection result and capability of not affecting the normal operation of a project, and is a nondestructive measurement method.