Time to positivity(TTP) is a new parameter in blood culture field.The article shows us the concepts of TTP,differential time to positivity (DTTP),and introduces their relation with bloodstream infection (BSI),catheter-related bloodstream infection (CRBSI).Besides,it stresses TTP' s clinical application,including determining the severity of disease;identifying the isolates whether pollution or not; identification of isolate strains ; detection of the drug resistance of isolates ; evaluating the effect of antibiotic ; helping to adjust the therapeutic drug; diagnosing or excluding CRBSI by means of DTTP;deciding whether the catheter is the source of infection in patients with candidemia; understanding the epidemiological distribution of strain.At the same time,the article also describes the shortcomings and domestic current status.