Abstract: In the present thesis,the program has been undertaken for the purpose how to realize the overall optimization of NLO properties-transparency-thermal stability via the rational molecular design.Since thienothiophene and its derivatives have smaller resonance energy and higher thermal stability,we design push-pull conjugated molecules featuring a thieno2,3-bthiophene as donor,connecting different receptor groups chromophores,using density functional theory method to study their electronic spectra and second-order NLO properties. And a number of optimized thienothiophthene derivatives chromophores have been obtained. The present study can provide a theoretical guide to the screening and experimental preparation of organic NLO materials.