The invention discloses a microwave single photon detector, detection method and preparation method thereof. It is equivalent to setting up two detectors sensitive to weak signals by embedding the Josephson junction in two arms of a power splitter. The statistical results of two arms recognition signals are obtained by multiple measurements, that is, the probability that the Josephson junction isin a voltage state and a ground state, and the number of microwave single photons detected by the Josephson junction. If the statistical results of the two arms conform to a certain coherence, the single photon detection is determined to be completed. The microwave single photon detector provided by the invention has the advantages of simple structure, high sensitivity and good stability, and thepreparation process thereof is relatively simple and low in cost. According to the microwave single photon detector and the detection method provided by the invention, efficient detection of a singlemicrowave photon can be achieved.