Based on gas sylphon, a novel dual-frequency laser accelerometer with double Y-shaped cavity is proposed. The static principle and the structure of the accelerometer are introduced. The influence of different factors on its resolution and their influencing mechanism are analyzed. As the first step sensing unit, the gas sylphon is used to translate the acceleration signal to the refractivity variation of the gas in it. The acceleration was measured in the form of the beat frequency of the dual-frequency laser in the end. The structure of optical module and physical property of the accelerometer are more stable due to this kind of ingenious design which also affords facilities for optimizing the parameters of the elastic sensing element. It becomes feasible to separate the signal from the noise because they affect the beat frequency through different ways. The original double Y-shaped cavity structure restrain the influence of the temperature noise to a great extent because of the first differential s and p light and the second differential of the symmetric double Y-shaped lasers. Theoretical analysis shows that the scale factor of the accelerometer is 1.19×108 Hz/(m/s2) and its resolution is 1.15×10-6 g.