The idea of primordial black holes (PBHs), first introduced by Stephen Hawking, is not only a possible solution to the dark matter problem, but also a unique tracer of the dynamics of inflation in the early universe. Also, PBHs are crucial to the study of black hole physics such as Hawking radiation. On the other hand, the discovery of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) opens the era of multi-messenger astronomy, and future networks of gravitational wave detectors will shed light on a new prospect of multi-band study of gravitational-wave universe. In this talk I will introduce our recent progress on such problems, including gravitational waves from binary PBHs, scalar-induced gravitational waves, neutrinos from Hawking radiation and accretions of PBHs.