The novel passive lossless soft-switching Cuk converter discussed in the paper aims to the following disadvantages of conventional turn-ON and turn-OFF snubbers(RLD/RCD):high switch losses, large peak current and peak voltage, low efficiency of conversion. Operation mode was analyzed, parameter design procedure was presented and a prototype of 400W was built and tested. The experiment results show that this converter can achieve turning on under ZCS and turning off under ZVS, switch losses are effectively reduced, the peak current and the peak voltage are lowered and the efficiency of the converter is improved.