A novel high-step-up DC/DC converter (HSUDC) is proposed and then the expression of power-loss calculation to estimate the efficiency of the converter is derived. The HSUDC can work at interleaved manner and mainly includes two power switches, four diodes, two coupled inductors and three capacitors. It can step up a low voltage to a much higher level for further grid-connection applications, which are therefore suitable to process the power generated by distrusted energy resources. Magnitude of power loss dominates the power density of a converter. Therefore, a theoretical and systematic estimation for HSUDC is developed, advancing the compact design towards converter building. Estimated results are compared with the practical measurements from a prototype to verify the correctness of the estimation.