Populations with diallele two-locus system were simulated with the Monte-Carlo method in order to examine the role of changing environment in retaining genetic variation under stabilizing selection. Without stabilizing selection the heterozygosities of the populations decreased slightly in 100 generations. Stabilizing selection without gene-environment interaction dropped the heterozygosities rapidly and depleted the genetic variation. A changing environment in which two alleles respond to environmental conditions in parallel, however, suppresses the tendency of stabilizing selection that depletes genetic variation. Certain intermediate environmental disturbance relates to community stability, and many endangered species show low genetic heterozygosities. Thus it is necessary to understand what kind of environmental changes will promote genetic variation. Environmental disturbance appropriate to the species to be conserved, therefore, should be incorporated into a preservation plan.