Field trials were conducted to study the influences of potassium(K)sources and application time on tuber yield，quality and K efficiency of rainfed and irrigated potato(Solanum tuberosum L.).Three K sources，i. e.potassium chloride (KCl)，potassium sulfate(K2SO4)，potassium nitrate(KNO3)，were selected and applied，respectively，at three times，i. e.totally base application，split(50% base application and 50% topdressing at flowering)and totally topdressing at flowering in the same rate of K.The control without K fertilizer was included.Results indicated K fertilization significantly increased tuber yield of rainfed and irrigated potato in Inner Mongolia site，compared with control without K，and base application or split application of KNO3 got the highest yield，but only base application of KCl significantly increased tuber yield in Gansu site.K fertilizers also increased K uptake，improved tuber quality，compared with control without K application.Multivariate analysis of variance showed that in rainfed and irrigated conditions there was no significantly different effect on tuber yield，K uptake，commercial rate，average tuber weight and starch content between K sources，but KCl in rainfed or KNO3 in irrigated condition resulted in lower reducing sugar content than K2SO4.Application times of K significantly affected tuber yield and K uptake of rainfed and irrigated potato.Base application of K produced more tuber yield，K uptake than totally topdressing and similar results to split application.KCl resulted in similar or higher agronomic efficiency of K(AEK)than K2SO4，and KNO3 resulted in a greater AEK than KCl and/or K2SO4 mainly in Inner Mongolia site.Base application of K resulted in higher AEK than split and/or totally topdressing.In summary，the response of potato yield and quality to KCl application was better than or equivalent to K2SO4 and KNO3.Base application of KCl could be recommended in potato production in experimental area.