Recent technological breakthroughs in single-particle cryo-electron microscopy (cryo-EM) enabled rapid atomic structure determination of biological macromolecules. A major bottleneck in the current single particle cryo-EM pipeline is to prepare good quality frozen cryo-EM grids, which often is a trial- and-error process. Among many issues, preferred particle orientation and sample damaging by air-water interface (AWI) are common problem in practice. Here we reported a method of applying metallo-supramolecular branched polymer (MSBP) in the cryo-sample preparation for high-resolution single-particle cryo-EM. Our data shows that applying MSBP keeps majority of particles away from air-water interface and mitigates preferred orientation, as demonstrated by analysis of both apoferritin and hemagglutinin (HA) trimer. Together, the use of MSBP is a simple method and could be applied to improve particle distribution for high-resolution structure determination using single-particle cryo-EM.