An hourly tidal level statistical method is proposed to calculate ridable tidal levels of seaports under the given tide rising duration and assurance rate.A bivarite variables of ridable tidal level and corresponding tidal duration are obtained from tide level history curve.The tidal levels data under given duration can be abstracted from the above bivariate.Then an accumulative frequency curve can be plotted from which the tidal level value under given assurance rate can be calculated.The results by new method are similar to those by technical code method,but the former method could reduce 50% of the calculation for plotting accumulative frequency curve.The computation time can also be reduced and the efficiency is increased.Both annual and seasonal ridable tidal high levels in Rizhao port have been calculated by using this new method.The result shows that the seasonal influences should be considered when ships take tide to enter Rizhao port.