An effective strategy for the controllable synthesis of single crystalline branched gold nanocrystals with a three-dimensional hierarchical structure was realized via the reduction of tetrachloroaurate ions (AuCl4-) assisted by the cationic surfactant poly(diallyldimethylammonium) chloride (PDDA) in acidic aqueous solution. The as-prepared gold nanostructures consisting of main trunks and almost symmetrical side branches presented a  plane and growth along the < 331 > direction. The PDDA and weak reducing agent, ascorbic acid (AA), were indispensable for the formation of these unique gold nanocrystals. The effects of HAuCl4 (or PDDA) concentrations, pH values and reaction temperatures on the morphology of branched gold nanocrystals are discussed in our work. A possible three-staged formation mechanism of initial branched nucleation, subsequent branched nanostructure growth and the final morphology adjustment was proposed on the basis of different reaction times and the corresponding changes in surface plasmon absorption. It is expected that the specific branched gold nanocrystals may find potential applications such as in optoelectronics, surface enhanced Raman scattering (SERS) and surface plasmonics.