The translation of English for science and technology (abbreviation for EST) in the internet era caters to the needs of the market and boasts a promising prospect. EST is a kind of informational text characterized by its scientific seriousness, requiring the translator to demonstrate the accuracy and logicality in translated text. Results show that the figure-ground theory can be well applied to spatial orientation analysis, temporal event analysis, and syntactic analysis. Regarding the complex sentences, Tamly put forward five principles of figure-ground theory including sequence principle, cause-result principle, inclusion principle, contingency principle and substitution principle. Taking petroleum EST as the research object, this paper applies the five related principles to the syntactic analysis of long and complex sentences with examples.