Based on the comparison between manual and automatic observations from 2012 to 2014 in Zhejiang province, the historical visibility and relative humidity data is amended and the haze day database is reconstructed according to "observational and forecasting measurement of haze". The linear trend of automatic visibility data is highly consistent with manual observations, while on average the automatic data is 28.6% less than manual observations. Their difference is greater in coastal areas. The relative humidity shows a significant downward trend since the beginning of automatic observation in 2004. The comparison between the daily manual and automatic relative humidity data at 20:00 shows that the average automatic data is 3% to 6% less than manual observation data. Linear regression is used for revising visibility and relative humidity data and the haze day database is reconstructed. After reconstruction, the bias between manual and automatic data is reduced and the new haze day database shows much higher quality with a uniform observational standard. The slightly polluted days show high consistency with the new haze days in 2013. The assessment of new haze day series in Zhejiang province shows that the number of haze days is relatively smaller in the 1970s and steadily increases in the 1980s, and reaches the highest in the 21^st century with the faster increasing rate. The center of haze day expands gradually from the middle-north to the north and the coastal areas in Zhejiang province, especially in major cities.