A general approach to controlled formation of microgels/nanogels is developed for producing hydrogel particles with customizable structures and properties, especially for fabricating multilayered hydrogel particles with flexibly designable structures and properties of each layer. An inverse emulsion technique is adopted to obtain micro- or nanodroplets of a disulfide-linked core/shell hyperbranched polymer. Then pH of the droplets is manipulated to trigger and control in situ core/shell separation of the polymer, dissociation of the shells, and cross-linking of the cores, in the confined space at micro/nanoscales. Loose and compact microgels/nanogels with diverse properties like particle size and swelling capacity are yielded via adjusting the gelation time. Multilayered hydrogel particles with each tailor-made layer are further prepared using the controlled in situ gelation method in association with a seed emulsion technique.