I will report the recent work from our group on the topic of primordial black holes. In this talk I will briefly review the standard mechanism of generating primordial black holes in the framework of cosmological perturbation theory. Then I will point out the deficit of the standard paradigm and introduce several latest mechanisms of the very early universe models. Afterwards, I will give a detailed description of how to generate primordial black holes in a much efficient way by taking into account the nonlinear resonance effect due to the sound speed parameter. This theoretical mechanism is promising to be falsified in the future astronomical observations.