Chirality evolution from molecule levels to the nanoscale in an achiral system is a fundamental issue that remains undiscovered. Here, we report the assembly of polyoxometalate (POM) clusters into chiral subnanostructures in achiral systems by programmable single-molecule interactions. Driven by the competing binding of Ca2+ and surface ligands, POM assemblies would twist into helical nanobelts, nanorings, and nanotubes with tunable helicity. Chiral molecules can be used to differentiate the formation energies of chiral isomers and immobilize the homochiral isomer, where strong circular dichroism (CD) signals are obtained in both solutions and films. Chiral helical nanobelts can be used as circularly polarized light (CPL) photodetectors due to their distinct chiroptic responsivity for right and left CPL. By the fine-tuning of interactions at single-molecule levels, the morphology and CD spectra of helical assemblies can be precisely controlled, providing an atomic precision model for investigation of the structure-chirality relationship and chirality manipulation at the nanoscale.