Sigma-delta beamformer (SDBF) was proposed in recent year to increase the integration level of an ultrasound imaging system. However, the hardware efficient post-delay reconstruction structure suffers from artifact problem when dynamic focusing is applied. A sigma-delta beamformer based on cascaded reconstruction has successfully corrected the artifact problem by reducing the pre-delay quantization noise level. Based on the same principle, we developed a multi-bit SDBF. The multi-bit SDBF provides comparable image quality as the pre-delay reconstruction SDBF without any extra artifact correction processing. It also reduces the operation frequency as well as the power compared to the single-bit SDBF. Real point and cyst phantom images are presented to compare the performance of the proposed beamformer with other existing techniques. Synthesis results shows that the proposed beamformer can save up to 78% of the power consumed by pre-delay reconstruction SDBF.