Current high-throughput DNA synthesis technologies use intricate chip and microfluidic systems to produce large-scale synthetic oligonucleotides but with low concentration and limited compatibility for long DNA assembly. Here we report a massive-in-parallel synthesis system, with an 'identification-sorting-synthesis-recycling' iteration mechanism applied to microchips for high-throughput DNA synthesis. This approach increases DNA product concentration by four to six orders of magnitude and simplifies downstream processes for large-scale gene synthesis.