In this paper, a K-band standing wave array waveguide slot antenna with a low sidelobe is designed, and the method of realizing low sidelobe is presented. The design sidelobe level is -27dB, and the slot amplitude distribution is calculated according to -30dB Taylor distribution. Using high frequency simulation software Ansoft HFSS, the normalized admittance of each slot is calculated, the simulation model is established and the antenna parameters are optimized. According to the results of the design, processing object and test the pattern and the gain, and the test results show that the antenna beam width about 3° within the working frequency band, the sidelobe level is less than 27dB, the working frequency band gain greater than 30.8dB, the simulation results are in conformity with the measured results, the design satisfies the requirement of indicators.