Based on real examples, this paper explains the concrete method and concept of Guarantee rate method, Frequency method,as well as Guarantee rate-Frequency method.

The designed minimum navigable discharges in the lower reaches of Ganjiang River are calculated by use of guarantee rate and frequency curves method, and the corresponding stages, namely the designed lowest navigable stages, are obtained from the stagedischarge relation curves in lowflow periods in recent years.

The substantial difference lies in that guaranteed rate frequency method determines the rate artificially, but synthetic duration curve method has its intrinsic frequency.

Based on real examples, this paper explains the concrete method and concept of Guarantee rate method, Frequency method,as well as Guarantee rate-Frequency method.

In allusion to the most outstanding pollution problem of water resources in northern China,on calculating method of basic environmental water requirement of the river function of depuration and dilution is proposed,namely,the monthly guaranteed frequency method.

The influent quality of the two existing wastewater treatment plants in Xi'an was investigated,and the methodology for determination of the influent quality as the basis for design of WWTP according to the frequency of pollutants concentration in wastewater(assurance rate of 85%)was put forward.

The article gets an optimization method of linear programming of elasticity constraints by using the content extent function and assurance rate.

The research indicated that,85% of assurance rate could be used to insure the effluent quality meet the standard.