A method and an apparatus for liquid safety-detection by backscattering with a radiation source are provided that relate to a radiation detecting technology field. The invention comprises using a radiation source, a collimator, a detector, a data collector and a computer data processor, and has the main steps of: 1) placing a liquid article to be detected onto a rotatable platform; 2) emitting a ray from the radiation source, said ray causing Compton scattering at the surface of the liquid after passing through the package layer of the liquid article; 3) the scattering photons being received by the detector after passing the collimator; 4) the detector transmitting the received data to the data collector; and 5) the data collector transmitting the amplified and shaped data to the computer data processor, which processes the data to obtain the liquid density of the detected article, then compares the result with the densities of dangerous articles in a current database, and gives a warning if the density of the detected article is consistent with that of a dangerous article. Compared to the prior art, the invention is convenient to use, detects rapidly and accurately, has a strong anti-interference, is very safe and reliable to use, and protection is easy.