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In general, the retrovirus particles become infectious on post-budding with cleavages of structural protein Gag by viral protease. Protease defective mutants bud particles normally, but the particles are non-infectious and called donuts-like particle because of their morphology. The viral genomes inside the donuts-like particles form very fragile dimer, which are far different from those in wild-type particles. The ordered particle maturation process is essential for infectivity of virus, but its mechanism largely remains unclear. We have constructed HIV-1 Gag cleavage site mutants to enable the steady state observation of virion maturation steps, and precisely study Gag processing, RNA dimerization, virion morphology and infectivity. As results, we found that these process progressed synchronously, but each transition point did not coincide completely. The mutual relationship between viral protein and RNA maturation is discussed for a further understanding of the retroviral life cycle.