The relation between unbiased estimation and direct computation in linear-moment method is introduced. The high correlation between each series in the process of computing probability weighted moments and its impact on the results were discussed. The approximate formula to directly compute Cv and Cs of linear moments was developed. The curve-fitting and the concerned plotting-position formula were described. In hydrologic frequency computation, due to the randomness of data and the summarization of processing techniques, the results obtained by any computed methods may contain the indetermination at different degrees. So, it can only be taken as initial values of estimation. The rationality analysis and modification have to be made after comprehensive balance in time and space. Then the results can be used.