The theoretical foundation is laid and the applied methods are demonstrated for the gravitational models of fractal cities. The generalised urban gravitation expression is derived out as Iij=GijMαiiMαjjr-bij by means of the geographical fractal theory, especially, the city size-output relationship, y=CPα. The parameters, α and b, are made clear to have some meanings of fractal dimension, and the gravitational ceofficient is defined as Gij=GCiCj｜Rij｜／(1+Sij),where G is a dimensional transformation coefficient, C is a proportional coefficient, Rij is a coefficient of correlation, and Sij is a coefficient of similarity. The gravitational theory developed by the authors in the paper is applied to the urban system of Changchun in Jilin and the cities of Zhengzhou, Kaifeng,and Luoyang in Henan, China, to show how to use the gravitation models in practice, and based on the examples mentioned above, it is discovered that the resultant of gravitational forces between a city and each of the other cities in an urbon system conforms to the rank-size rule in due conditions, i.e., Fi(k)=F1k-q,where is rank, and F1 and q are parameters.