He had been the Mallinckrodt Professor of Chemistry and Chemical Biology at Harvard University until 2018, when he became the Lee Shau-kee Professor of Peking University. He was the Director of Biomedical Pioneering Innovation Center (BIOPIC) in 2010-2021, and the Director of Beijing Advanced Innovation Center for Genomics (ICG) in 2016-2021, both at Peking University.
As a pioneer of single-molecule biophysical chemistry, Coherent Raman scattering microscopy, and single-cell genomics, he made major contributions to the emergence of these fields. Furthermore, he has made significant advances on medical applications of label-free optical imaging and single-cell genomics. In particular, his inventions in single-cell genomics have been used in in vitro fertilization benefited thousands of families by avoiding the transmission of monogenic diseases to their newborns.
More than fifty of his students and post-doctorates have become professors at major universities around the world, and two are co-founders of start-up companies.
Professor Xie’s current research interests include the following scientific, technological, and medical areas:
* Scientific: Single-molecule enzymology, Single-molecule biophysical chemistry, Gene expression and regulation, Epigenetics, Mechanism of cell differentiation and reprogramming, Chromosome structure and dynamics, and Genomic instability; 
* Technological: Single-molecule imaging, Single-cell genomics, Coherent Raman scattering microscopy, DNA sequencing; 
* Medical: Preimplantation genetic testing in in vitro fertilization, COVID19 vaccine and neutralizing antibody drugs for SARS-CoV-2 variants and Early cancer diagnosis.