Abstract: Abstract: The daily reference evapotranspiration (ET0) is generally demanded in the application of agriculture, meteorology, hydrology and other fields. The calculation of daily ET0 based on the data of different time resolutions is always a simplification because the change of ET0 is a continuous process in the time scale. It is valuable to discuss the influence of the simplification with different time resolutions on the accuracy of ET0 estimation. In this paper, based on the observed data of Shouxian National Climate Observatory from 2007 to 2013, the daily average values were calculated using the data with the resolution of 1 minute as the true values. The effects of the 7 different time resolutions (including 10 min, 20 min, 30 min, 40 min, 60 min, 4 times per day and 3 times per day) on the estimation of daily air temperature, wind speed, solar radiation, relative humidity and daily, monthly, yearly reference evapotranspiration (ET0) were analyzed by the error comparison. Results showed that the absolute values of the errors for ET0 and 4 climatic variables increased with the lower time resolution. Wind speed was most sensitive to the change in the time resolution, followed by solar radiation. The mean absolute relative errors (MAPE) of wind speed were 1.35%, 2.20%, 2.79%, 3.54%, 4.48%, 16.01% and 24.29% for the time resolution of 10 min, 20 min, 30 min, 40 min, 60 min, 4 times per day and 3 times per day, respectively. The change in the time resolution showed less influence on daily air temperature and relative humidity than the other 2 factors. The MAPE values of daily ET0 were 0.53%, 1.01%, 1.38%, 1.72%, 2.46%, 4.72% and 6.14% respectively for the 7 time resolutions, indicating that the accuracies of ET0 estimation for 3 and 4 times per day were significantly lower than the other 5 time resolutions. Over 95% of the absolute errors for daily ET0 with the time resolution from 10 to 40 min were in the range of -0.20-0.20 mm/d. These errors were so small and concentrated that the meteorological data with these 4 time resolutions were suitable for daily ET0 estimation. The mean bias errors (MBE) were almost equal to 0 for the time resolutions from 10 to 60 min, and the total deviation degree was very low. The MBE value for 4 times per day was -0.01 and the estimated ET0 was smaller than the true value, while the MBE value for 3 times per day was 0.02 and the estimated ET0 was larger. The change in the time resolution of the solar radiation led to the largest attribution to the error of estimated ET0, followed by wind speed, because these 2 climatic factors were more sensitive to the change in the time resolution and they were the key factors to the radiation item and dynamic item of ET0 respectively. The absolute values of the errors of monthly and yearly ET0 were significantly less than that of daily ET0. The MAPE values of monthly ET0 were 0.13%, 0.21%, 0.27%, 0.40%, 0.50%, 1.18% and 1.48% respectively for the 7 time resolutions. The absolute values of the relative error of yearly ET0 were mostly less than 0.50%. Our study demonstrated that the change in the time resolution of meteorological variables showed less impact on the estimation of the long-term integrated ET0 and it was important to improve observation time resolution for increasing the ET0 estimation accuracy.