Abstract:In the Ps score assessment, the forecast skills are determined by the difference between Ps score of operational forecast and random forecast accuracy over a period of time. The paper attempts to make quantitative evaluation of the random forecast accuracy among all the provinces and regions in China， and the statistical results are as follows. (1) Owing to the obvious difference of the random forecast accuracy about station elements determined by climate probability in each grade in every province, the maximum difference of precipitation score is 14, and the maximum difference of temperature score is 7. (2) Since the judging standard of forecast accuracy has been designed vulnerably, the accuracy of two grade forecast and continuous forecast may be higher than random forecast accuracy, it brings uncertainty to the quantitative evaluation of random forecast accuracy; (3) The score of random forecast might be higher than that of the actual forecast if these factors affecting the score are applied to quantitative assessment. The result shows that the current scoring methods could not access the forecast skills in various provinces properly.