Darwinian evolutionism with its core concept of natural selection as one of the greatest achievements in natural science has largely been challenged recently due to lack of biological ontology. A universal physical principle for biological evolutions with her own ontology is highly needed. Basing on a new informational reality of generalized genotype or phenotype ontology for biological systems, this paper proposed maximum flux principle (MFP) as a universal physical principle for biological evolutions to reveal underlying mechanisms. The evolutionary dynamics of biological systems are further simulated by typical examples. The validity of this new model for biological evolutions is checked. Analyses basing on evolutionary process underpinned by MFP are advantageous over available approaches.