Lg wave propagation characteristics are investigated in Northeast China and the Korean Peninsula based on seismograms from 113 crustal earthquakes that were recorded at 602 regional stations distributed throughout eastern China, South Korea, and southern Japan. Based on 22,551 vertical component waveforms, we calculate the amplitude spectra of the Lg waves, extract the single station, two-station, and two-event data, and construct a broadband Lg attenuation model between 0.05 and 10.0 Hz in Northeast China and the Korean Peninsula by using a joint tomographic method to simultaneously obtain Q, source function, and site response. Results show that the sedimentary basin areas are characterized by relatively strong Lg attenuation, whereas the volcanic mountains such as Da Hinggan Ling and Changbai mountains attenuate the Lg waves weakly. The strongest Lg attenuation regions are areas covered by sea water including Bohai Sea, Yellow Sea and Japan Sea. A thinner crust within a typical oceanic lithosphere for the Japan Sea blocks the Lg wave propagation, resulting in no signals can be observed across oceanic path from small earthquakes. We collect observations from large earthquakes with magnitude around m(b) 6.0 to obtain strong Lg attenuation within the crust of Japan Sea.