Based on the formula of flow deviation rate proposed by authors in reference [10], the further derivation was conducted to simplify the parameters in the formula for designing drip irrigation system economically and credibly. According to the hydraulic analysis using step-by-step method, the integrated flow deviation rates for a drip irrigation submain unit were calculated at different emitter manufacturing variation. The formula of flow deviation rate was verified by the statistical analysis of the integrated flow deviation rate. Further, the effect of emitter manufacturing variation on integrated flow deviation rate was analyzed using the formula, and the allowable value for integrated flow deviation rate of drip irrigation submain unit was recommended for drip irrigation system design.