Several frontiers of animal life history evolution field are reviewed in this paper: life history traits, life history strategy, trade-offs, fitness and evolutionary demography. Life history traits are linked by trade-offs, which are composed of physiological trade-offs and evolutionary trade-offs. Fitness is related with specific environmental condition, and it is closely connected with the evolution of life history trait. There have been many hypotheses analyzing animal life history strategy, of which r-Strategy and K-Strategy theory provided by MacArthur and Wilson is most influential. Senescence refers to the decline of survival rate and reproductive rate of individuals with age. There are two hypotheses explaining the evolution of ageing, i.e. mutation-selection balance hypothesis and antagonistic pleiotropy hypothesis. Evolutionary demography, which applies demographic techniques into the analysis of life history evolution, provides a powerful approach for the research of fitness of phenotype evolution. The greatest challenge for contemporary evolutionary ecologists is to construct an integrated theoretic system combined by evolutionary demography, quantitative genetics, and lineage-specific effect theory in the future research of animal life history evolution.