In order to reduce the two main vibration frequency of the variable speed helicopter, an anti-resonance vibration isolator with double frequency vibration isolation is designed. First, the dynamic formula of the dual frequency vibration isolator was deduced based on the traditional dynamic anti-resonance theory. With the formula, the natural frequency, antiresonant frequency and transmissivity of the isolator are obtained. Then, the sensitivity of the performance and efficiency for the isolator is analyzed. The effects of design parameters such as secondary spring stiffness and secondary vibration isolation mass on the natural frequency and vibration isolation frequency of the isolator are obtained. The property test and vibration test are carried out. The calculation and test results show that the isolator has two vibration isolation frequency. The secondary vibration isolation efficiency is more than 60%, and the antiresonance frequency and efficiency of the isolator are both affected by the design parameters.