1. A method for evaluating attention degree in a three-dimensional (3D) virtual world, the 3D virtual world comprising at least one virtual object and at least one avatar controlled by a user, the at least one avatar having a corresponding avatar view field, the method comprising: dividing a scene in the 3D virtual world into a plurality of lattice cells each designating an area of interest, each area of interest having a size dependent upon a number of virtual objects and avatars therein, wherein areas of interest having a larger number of virtual objects and avatars have a larger size in comparison to areas of interest having a smaller number of virtual objects and avatars; determining an association of virtual objects that are contained in each area of interest; applying an index to each area of interest; recording the association between the virtual objects in each of the areas of interest in a correspondence table per the indexes, the correspondence table containing a correspondence relationship between each area of interest and the virtual objects contained therein, information in the correspondence table is updated as positions of the virtual objects change within the areas of interest; obtaining geometrical information about the avatar view field and geometrical information about the at least one virtual object, wherein the obtaining of geometrical information about the at least one virtual object includes receiving a position and number of virtual objects in each area of interest from the correspondence table, the avatar view field represented by a pyramid having a vertex position Pe, an axis direction vector Ve extending from the vertex position Pe, an elevation angle Θ formed between lines in the pyramid that intersect at the vertex position Pe, and a distance D 2 measured from the vertex position Pe that is indicative of a farthest distance point of the avatar view field, the at least one object represented by a distance D from the vertex position Pe, and an angle α formed between a line connecting the at least one object and the vertex position Pe and the axis direction vector Ve; determining an association between the avatar view field and the at least one virtual object based on the geometrical information, wherein the determining of an association between the avatar view field and the at least one virtual object based on the geometrical information includes determining a relative position of the at least one virtual object with respect to the avatar view field, wherein the relative position is determined as a function of D/D 2 and α/Θ; evaluating an attention degree of the at least one virtual object based on the association, wherein the attention degree is based on the relative position of the at least one virtual object with respect to the avatar view field; and providing an evaluation result for the attention degree of the at least one virtual object, wherein the evaluation result comprises a score indicative of the attention degree of the at least one virtual object, the score of attention degree defined as: 
 S=a D 2/ D+b Θ−α/Θ, wherein a and b are settable positive parameters, D 2 /D reflects an influence of the relative distance D such that a smaller relative distance D results in a higher score S, and Θ−α/Θ reflects an influence of the relative angle α such that a smaller relative angle α results in a higher score S.