The invention discloses a radiator leak detector and a method for assembling and applying the same. The radiator leak detector comprises a pressure gauge and connecting pipes. The connecting pipes include a first connecting pipe and a second connecting pipe, one end of the first connecting pipe is connected with a barrier, the other end of the first connecting pipe is connected with one end of a bent pipe, the other end of the bent pipe is connected with one end of a valve by the second connecting pipe, and the other end of the valve is connected with the pressure gauge; the valve is a three-way copper valve, two valve ports, which are positioned on the same horizontal line, of the three-way copper valve are connected with the pressure gauge and the second connecting pipe, and another valve port of the three-way copper valve is connected with an inflator pump; external threads are arranged at two ends of the first connecting pipe and two ends of the second connecting pipe, internal threads are arranged on the inner sides of a left port and a right port of the bent pipe, and the sizes of the internal threads on the bent pipe are matched with the sizes of the external threads on thefirst connecting pipe and the second connecting pipe. The radiator leak detector and the method have the advantages of simplicity in assembling and convenience in use.