The trustworthy of software mainly depends on the trustworthy of source codes. Some factors including defects,errors and program faults in the source codes,virus from outside and malicious codes etc decide the trustworthy of software, so guaranteeing the trustworthy of software from aspect of source code is one of the most important methods for ensuring the trustworthy of software. As a kind of the most important system software, the trustworthy of compiler plays a critical role in the whole computer system. The software program can only be executed after compiled by compiler, so if the compiler can not be trusted, the trustworthy of executable code outputted can not be guaranteed. The key technologies and thoughts for developing trusted compiler are discussed in this paper.