Abstract: Abstract: Ritchie model is popular for evaporation estimation, but it needs to be modified before use in local regions, especially in saline alkaline soil. This study carried out a field experiment to modify the coefficient of Ritchie model. The experiment was carried out in bare field of Daqing City in August and September of 2015. The city had annual precipitation of 427.5 mm and annual evaporation of 1635 mm. The soil was sandy loam. A micro-lysimeter was used for evaporation measurement in bare soil. The lysimeter was 2 mm in thickness, 150 mm in height, and 74 mm in inner diameter. The soil in the lysimeter was replaced every 7 days, and after raining. The effects of rainfall and relative humidity on evaporation were analyzed since the other factors such as temperature and wind speed was similar for the 2 months in the study. The results showed that the relationship between evaporation and relative humidity in these 2 months was similar. The maximum relative humidity was 61% and 43% in August and September, and the mean evaporation was 5.2 and 6.2 mm/d in August and September, respectively. For using Ritchie model, the evaporation limit of the first stage was designed as 8 mm. Using the coefficient value from literature 4.62 mm/d0.5, the model yielded a relatively low evaporation estimation (R2=0.61). Randomly selecting data on 18th-19th in August and on 1st-7th in September, the model coefficient was determined as 2.81 and 0.01 mm/d0.5 for August and September, respectively. Validation using the other data showed that the measured and calculated evaporation values based on the revised coefficient were closely linearly correlated with R2 0.94. The root mean square error was decreased from 3.04 to 0.44 mm/d. Validation using measured evaporation values from maize field in 2016 showed that the measured and calculated values based on revised coefficient were linearly correlated with R2 0.95. Thus, the revised coefficient showed high reliability for evaporation estimation in the study area.