Objective To verify the reliability of home blood pressure measurement in clinic and research works by comparison three methods[home(H),office(O) and ambulatory(A)]of blood pressure(BP) measurements. Methods The"study-effects of salt substitution on blood pressure among the hypertensive patients and their families"was a randomized,double blinded control trial.In this study,BP was measured in 220 hypertensive patients using office,home and ambulatory BP measurements concurrently at the baseline and the end of the intervention. Two hundred seventeen patients had baseline eligible data,while at the end of the intervention,only 189 patients had eligible data.Bland-Altman method and Person's correlation analysis were used to compare the agreement of BP levels by 3 methods,and McNemar chi-square test compared rates of the agreement,assuming the ambulatory as the reference.Results The mean BP levels using office,ambulatory and home BP measurements were 149.5?16.4/87.2?9.5 mm Hg,137.8?17.1/83.2?10.3 mm Hg,and 138.0?14.2/82.4?9.3 mm Hg,respectively. H BP was more strongly related with ambulatory BP(SBP/DBP)(H:r=0.55/0.62 vs O:r= 0.36/0.46).The difference of BP between H and A was smaller[H:A—0.2 mm Hg/—0.7 mm Hg vs O:A(ll.7 mm Hg/4.0 mm Hg)].Intra-individual agreement between H and A SBP was significantly higher than that between O and A(28.3%vs 16.5%for≤|5| mm Hg and 49.7%vs 33.5%for≤|10| mm Hg,all P0.05).Conclusion Home and ambulatory BP was more strongly related and better agreement than office-ambulatory BP measurement.