The lack of evidence for weak scale supersymmetry (SUSY) from LHC Run-I at √s = 8 TeV and Run-II with √s = 13 TeV results have caused a paradigm shift in expected phenomenology of SUSY models. The spectrum of sparticle (SUSY particle) masses has been pushed to a higher, multi-TeV energy scale. The spectrum was predicted to lie not too far beyond the weak scale typified by Z and W masses based on naturalness in pre-LHC years. In such models, the neutralino (the lightest SUSY particle) can account for the measured dark matter (DM) relic density. At the higher mass scale, correct relic density can only be obtained by enhanced annihilations or more naturally, by a low μ term. Although it has not been discovered at the colliders yet, SUSY still remains the most attractive solution for the big hierarchy problem. In this thesis, I investigate SUSY models with mixed axion-neutralino dark matter with two MSSM scenarios: CMSSM (with a standard neutralino overabundance) and NUHM2 (with a standard neutralino underabundance). The NUHM2 model with a low μ gives a natural SUSY spectrum defined by the ∆EW measure. Phenomenological implications of the two component dark matter scenarios are studied in detail.