A model of non-uniform height rectangular fin, in which the variation of base’s thickness and width are taken into account, is established in this paper. The dimensionless maximum thermal resistance(DMTR) and the dimensionless equivalent thermal resistance(DETR) defined based on the entransy dissipation rate(EDR) are taken as performance evaluation indexes. According to constructal theory, the variations of the two indexes with the geometric parameters of the fin are analyzed by using a finite-volume computational fluid dynamics code, the effects of the fin-material fraction on the two indexes are analyzed. It is found that the two indexes decrease monotonically as the ratio between the front height and the back height of the fin increases subjected to the non-uniform height rectangular fin. When the model is reduced to the uniform height fin, the two indexes increase first and then decrease with increase in the ratio between the height of the fin and the fin space. The fin-material fraction has no effect on the change rule of the two indexes with the ratio between the height of the fin and the fin space. The sensitivity of the DETR to the geometric parameters of the fin is higher than that of the DMTR to the geometric parameters. The results obtained herein can provide some theoretical support for the thermal design of rectangular fins. A model of non-uniform height rectangular fin, in which the variation of base’s thickness and width are taken into account, is established in this paper. The dimensionless maximum thermal resistance (DMTR) and the dimensionless equivalent thermal resistance (DETR) defined based on the entransy dissipation rate (EDR) are taken as performance evaluation indexes. the variations of the two indexes with the geometric parameters of the fin are using by a finite-volume computational fluid dynamics code, the effects of the fin it is found that the two indexes decrease monotonically as the ratio between the front height and the back height of the fin increases to the non-uniform height rectangular fin. When the model is reduced to the uniform height fin, the two indexes increase first and then decrease with increase in the ratio between the height of the fin and the fin space. The fin-material fr action has no effect on the change rule of the two indexes with the ratio between the height of the fin and the fin space. The sensitivity of the DETR to the geometric parameters of the fin is higher than that of the of DMTR to the geometric parameters. The results obtained herein can provide some theoretical support for the thermal design of rectangular fins.