It has becoming a developing trend to replace boilers with heat pumps driven by electricity under the global carbon neutrality strategy. The exergy loss and thermal performance of the conventional circulating flash heat pump steam generator (CF-SGHP) system were researched. A new direct evaporative heat pump steam generator (DE-SGHP) system was proposed in order to reduce total exergy loss. Then the exergy loss and thermal performance of the two systems was analyzed comparatively under different discharge steam temperature (T out ), condensation temperature (T cond ) and heat source water temperature (T hsw ). The results are as follows: The exergy efficiency (ƞ ex,sys ) of the CF-SGHP system is 62.98%. In addition to the exergy loss caused by the irreversible process of the compressor, the relative maximum exergy loss occurred in the flash cycle process, whose exergy loss rate is 23.24%; The exergy loss of DE-SGHP system is always lower and the COP is always higher than that of the CF-SGHP system within the range of T out , T cond and T hsw ; There existed an optimal T cond of 91 ℃ in the DE-SGHP system to maximum the ƞ ex,sys of 67.74% and the COP of 2.71 when T out is 165℃ and T hsw is 60℃, that indicated to have a broader development prospect.