Dynamic variable delay range is the very important performance for an optical buffer. This paper establishes an analysis model for the optical buffer of double loop configuration based on collinear 3×3 fiber coupler and analyzes the limiting factors which define the double loop optical buffer (DLOB)′s delay range. Numerical simulations find that a large dynamical variable delay range can be realized by cascading DLOB. The experiment demonstrates that a large delay variation of 1-9999 times of basic delay unit,the fine granularity of 25 ns and the BER of the output data is as low as 10-9. The theory model and analytical method obtained in this paper can also be used to analyze other optical switches based on SOA.