The invention provides an on-chip soft start circuit and a power converter, the on-chip soft start circuit comprises a current source, a soft start capacitor, a switch connected in parallel with two ends of the capacitor, a first resistor, a conversion circuit and a boost circuit, through multiple on-off control of the switch, charge and discharge control of the soft start capacitor is realized, and meanwhile, the on-chip soft start circuit is connected with the power converter. In the charging and discharging process, the output voltage of the on-chip soft start circuit gradually rises to the preset reference voltage, the switch stops discharging, finally, a voltage signal in a corresponding rising curve is output to a DC-DC converter in the power converter, the duty ratio of a PWM signal is gradually adjusted, the increase of overshoot current is restrained, and soft start protection work in the preset time length is achieved.