An innovative cascaded double-loop optical buffer (DLOB) with a large dynamic variable delay suitable for buffering multichannel data packets is proposed and demonstrated. In this buffer, the pure phase modulation of the gain-transparent semiconductor optical amplifier (GT-SOA) is used as the optical switching, and then an experimental system with two buffering units is established. The data packets carried out on four different wavelengths have been stored for 12 round trips successively in DLOB1 and DLOB2, and a long delay time of 39.6 μs has been achieved. The pulse distortion, pattern effect, and channel crosstalk caused by the SOA’s nonlinear gain, carrier recovery time, cross-phase modulation, and cross-gain modulation have been eliminated clearly, and the accumulation of ASE noise has also been effectively mitigated. The signal details, the eye diagrams, and the bit error ratio curves for all four wavelengths show that the proposed optical buffer is an effective approach for buffering multichannel data packets, especially when the GT-SOA’s transmission loss decreases in the near future.