Among the changes approved was the addition of the phrase "respecting and protecting human rights" written into the law's first chapter concerning the law's basic principles, China's state-run Xinhua news agency reported.
However, changes to the Criminal Procedure Law also allow police to hold certain suspects at secret locations for up to six months, CNN said.
Critics said the overhaul of the code -- hailed in the Chinese-run media as a victory for human rights -- still leaves room for abuses by granting more power to China's already powerful state security operation.
Under the changes to the Criminal Procedure Law passed Wednesday by the National People's Congress, the police will have the authority to hold suspects for up to six months at undisclosed locations if they believe the detainees are involved in national security endangerment, terrorism or egregious bribery, CNN said.
Xinhua reported the revised law clarifies that confessions obtained through illegal means, and illegally obtained witness testimony and depositions of victims should be excluded at trial, parliamentary officials said.
"The [goal] of this revision is to better embody the constitutional principle of respecting and protecting human rights," said Wang Liming, deputy president of Renmin University of China and a deputy with the National People's Congress, China's parliament.
Human rights advocates have expressed doubt about how well the revised code will be respected, CNN said.
"The test will really be in the implementation," said Nicholas Bequelin, senior researcher for Human Rights Watch. "The police are already violating and willfully ignoring many of the defendant's rights under the law."
Chinese Internet users also raised alarm about the law after it passed on a lopsided 2,639-160 vote.
"This is such retrogression," blogger "Luoguogg" wrote. "Can't believe I'm seeing a dark moment in history with my own eyes."