We present a newly developed macromolecular ion accelerator mass spectrometer that combines a dual-ion-trap device and a macromolecular ion accelerator (MIA) to achieve the capability of analyzing samples with a mixture of large biomolecules. MIA greatly increases detection efficiency. The dual ion trap includes a quadrupole ion trap (QIT) and a linear ion trap (LIT) in tandem. The dual ion trap is mounted ahead of the MIA. The QIT is used to store multiple species, and the LIT is employed to capture the ions that are sequentially ejected out of the QIT. Subsequent to their capture, the ions inside of the LIT are extracted and transferred to the MIA. The synchronization between the QIT and MIA is bridged by the LIT. A sample containing a mixture of several large biomolecules was employed to examine the performance of this new type of mass spectrometer. The result reveals that larger biomolecules show a comparable signal to smaller biomolecules, even though the mixture contains equal quantities of each type of protein. The overall assembly produces a nearly constant detection efficiency over a broad mass range. Thus, this device provides an alternative platform to analyze complex large-protein mixtures.