Abstract: In the report, in order to analyze the variation law of negative oxygen ion concentration in Haikou crater national geological park and its correlation with environmental and meteorological factors, and provide some references for the study of negative oxygen ion concentration in China’s tropical monsoon climate zone, the arithmetic mean value method was used to analyze the hourly negative oxygen ion observation data from Haikou environmental protection monitoring station, the annual/seasonal mean and hourly mean of Haikou crater national geological park from 2016 to 2017; SPSS single-factor Pearson correlation analysis method was used to analyze the observed influencing factors in different seasons; the data statistical analysis and EIAProA2008 were used to analyze the relationship between humidity, wind direction, wind speed and negative oxygen ion concentration. The results showed that the average concentration of negative oxygen ions in Haikou crater national geological park is 1327 ion·cm^-3 in 2016 and 1662 ion·cm^-3 in 2017; the concentration of negative oxygen ion is higher in Summer and Autumn than that in Spring, with its minimum value in Winter; the concentration of negative oxygen ion at day is higher than that at night, the maximum value appears at day while the minimum value appears at night;the negative oxygen ion concentration is negatively correlated with sulfur dioxide, PM10 and PM2.5 in ambient air, and positively correlated with temperature, on the whole, it is negatively correlated with humidity, but positively affected by humidity in a short time; when the wind direction is taken as a reference, the concentration of negative oxygen ions in the upwind direction is negatively correlated with the wind speed, while negative oxygen ions in the downwind direction are positively correlated with the wind speed. Our findings provide theoretical reference for further research on the characteristics and influencing factors of negative oxygen ion concentration in tropical areas of China.