By use of an observed data series a new dynamic data modeling has been proposed.Taking a nonlinear ordinary differential equation which is retrieved from the data series based on the bilateral difference principle as a dynamic kernal, with the self-memorization principle one can establish a forecast model,which is called data-based mechanistic self-memory model (abbreviation DAMSM) .Some computing cases show that the forecasting accuracy of the DAMSM is quite satisfactory,the inter-annual precipitation forecast insummer over Yangtze Delta is presented.