Abstract: Objective To investigate dose-response relationship between daily concentration of particulate matter <2.5 microm in aerodynamic diameter (PM_2.5) and daily mortality rate and to provide a scientific basis for evaluating health impact of severe fog and haze.Methods Domestic epidemiological studies on PM_2.5 and mortality were collected with systematically searching through China National Knowledge Infrastructure (CNKI),PubMed Database and Elsevier Science Direct Database.Stata 12.0 software was adopted to conduct a meta-analysis on short-time impact of PM_2.5 on mortality using inverse variance (I-V) weighting method.Results A total of 11 literatures (one published in Chinese and 10 in English) were finally extracted,including 13 studies in six cities (Shanghai,Xi'an,Beijing,Shenyang,Guangzhou,and Chongqing).The results of meta-analysis show that a 10 μg/m³ increase in daily PM_2.5 concentration is related to a 0.37% (95% confidence interval95% CI:0.26%-0.48%) increase in daily mortality rate.Subgroup analyses show that a 10 μg/m³ increase in daily PM_2.5 is related to a 0.33%(95%CI=0.20%-0.46%) increase in daily mortality rate under the condition of relative higher average daily PM_2.5 ≥75 μg/m³;while under the average daily PM_2.5 concentration of <75 μg/m³,a 10 μg/m³ PM_2.5 increase is related to a 0.50%(95%CI=0.36%-0.63%)daily mortality rate increase. The results of subgroup analysis also show that under a relative higher ambient temperature (in Southern China),a 10 μg/m³ PM_2.5 increase is related to a 0.51%(95%CI=0.32%-0.69%) daily mortality rate increase,but the same increase in PM_2.5 is related to a 0.35%(95%CI=0.23%-0.47%)increase in daily mortality rate under a relative lower ambient temperature (in Northern China).Conclusion Increase in PM_2.5 concentration may relate to short-term increase in daily mortality rate among urban populations.