After the comparing of the weather factors,predicting method and ratings standard for urban fire research and operation all over the country,five weather factors are selected for the research: daily minimum relative humidity(index 0-40),number of consecutive days without precipitation(index 0-30),daily maximum air temperature(index 0-20),daily maximum wind strength or velocity(index 0-20) and daily rainfall(index 0-20),and the complex index generally range from 0 to 100 and can be divided to five ratings from low to high.Two experiments are designed to optimize the effect of ratings division: 1) daily fire-danger ratings in four typical months of 2001 for 5 cities from north to south in China are calculated by using above method and local method and compared,and the index with factors are adjusted to make coincidence ratio of two daily rating sequence higher and the correct ratio of ratings ≥85%(supposed that the predicting value has only one or no rating error with actual rating;2) the total number of every rating for thirteen central cities in China from 2000 to 2003 are calculated and made to fit with the normal distribution.Then,the dividing range of weather factors,corresponding urban fire-danger index and ratings are determined,and the ratings are named.