Abstract: Chloroplasts, the special organelles present in plant and algal cells, are responsible for converting light energy into chemical energy through photosynthesis. The majority of chloroplast proteins are encoded by nuclear genes. And the precursor proteins (preproteins) are synthesized by the 80S ribosomes in cytosol. Subsequently, guided by the transit peptides, preproteins are delivered into the chloroplasts through the post-translational translocation pathways across the outer and inner envelop membranes to fulfill their biological functions inside the chloroplasts. The central route for the preproteins to enter the chloroplast mainly relies on the synergistic action of the translocons in the outer and inner envelope membranes of chloroplasts (TOC and TIC). Here we review the recent research progress on structural biology studies of the TOC-TIC supercomplex and discuss the functional characteristics of its components, potential pathways for precursor protein translocation into chloroplasts, and the regulatory mechanisms.