Nowadays　phase　change　materials　(PCMs)　have　been　used　in　preliminary　practical　engineering.　However,　the　selection　of　the　thermal　design　parameter　of　PCMs　is　really　difficult　on　account　of　the　change　of　specific　heat　capacity,　thermal　conductivity　in　phase　change　region　and　the　impact　of　the　latent　heat.　Thermal　conductivity　can＇t　be　used　in　the　selection　of　PCMs.　To　provide　guidance　in　thermal　design　of　the　wall,　relative　thermal　conductivity　(RTC)　of　the　PCM　layer　was　defined　and　its　computing　method　was　given.　RTC　is　a　thermal-physical　parameter　that　can　represent　the　same　heat　transfer　capacity　of　PCMs　with　that　of　normal　materials　in　the　same　conditions.　Based　on　the　computing　method,　RTC　of　the　PCM　layer　in　different　areas　were　calculated,　and　heat　transfer　characteristics　of　PCM　layers　in　the　whole　year　were　shown.　In　addition,　PCM　layers＇　utilization　effects　in　different　areas　of　China　were　analyzed.　By　comparing　different　PCM　layers＇　RTC,　it　was　obtained　that　different　layers　had　different　utilization　effects.　RTC　can　be　used　to　select　the　proper　PCM　used　in　a　certain　area.　©　2017,　Editorial　Board　of　Journal　of　Harbin　Institute　of　Technology.　All　right　reserved.