Temporarily storing light occupies a pivotal position in all-optical packet switching network and microwave photonics. An integrated optical buffer with large capacity and low loss is demonstrated on a silica wafer. The optical buffer consists of four silica waveguide delay lines connected by five thermo-optic switches. With different switch combinations applied, related delay lines are selected to realize a different storage time in the buffer, and a storage time up to 100 ns with a 10-ns step size is implemented. By optimizing the fabrication process and introducing the offsets between straight and bending waveguides, the propagation loss as low as ~1.08 dB/m is achieved. This large-capacity and low-loss buffer enables broad applications in optical communications and microwave photonics.