On　the　basis　of　exergetic　analysis,　ecological　performance　analysis　and　optimisation　of　an　endoreversible　simple　air　heat　pump　cycle　with　constant-temperature　heat　reservoirs　is　carried　out　in　this　paper.　An　exergy-based　ecological　optimisation　criterion,　which　consists　of　maximising　a　function　representing　the　best　compromise　between　the　exergy　output　rate　and　exergy　loss　rate　(entropy　generation　rate　and　environment　temperature　product)　of　the　heat　pump　cycle,　is　taken　as　the　objective　function.　The　analytical　formulae　concerning　the　relationship　between　the　exergy-based　ecological　function　and　pressure　ratio　is　derived　with　heat　resistance　losses　in　the　hot-　and　cold-side　heat　exchangers.　The　effects　of　the　effectivenesses　of　the　heat　exchangers,　the　ratio　of　hot-side　heat　reservoir　temperature　to　ambient　temperature　and　the　heat　reservoir　temperature　ratio　on　the　exergy-based　ecological　function　are　analysed.　The　cycle　performance　optimisations　are　performed　by　identifying　the　optimum　pressure　ratio　and　the　optimum　distribution　of　heat　conductance　of　the　hot-　and　cold-side　heat　exchangers　for　a　fixed　total　heat　exchanger　inventory,　respectively.　The　expressions　of　the　maximum　ecological　function　are　derived.　The　influences　of　some　design　parameters,　including　heat　capacity　rate　of　the　working　fluid　and　heat　exchanger　inventory　on　the　optimal　performance　of　the　endoreversible　air　heat　pump　are　provided　by　numerical　examples.　The　results　show　that　exergy-based　ecological　optimisation　is　an　important　and　effective　criterion　for　the　evaluation　of　air　heat　pumps.　©　Ambient　Press　Limited　2009.