A two-dimensional, time-dependent and warm cumulus cloud model has been used to investigate problems concerning cloud merger and interaction. The results of numerical experiment show: (ⅰ) Two clouds formed at the same time have influence on each other at a shorter distance;on one hand, it is possible that they merge with equal intensity, and on the other, it is impossible that they merge with unequal intensity;in case of quite different intensities the weak cloud is depressed and the strong cloud accretes. (ⅱ) Two clouds, developing with timing difference at a shorter distance and in the same growth stages, may merge. (ⅲ) The merged cloud develops more violently than the unmerged and produces more rainfall. (ⅳ) Cloud merger results from the action of a horizontal pressure gradient accompanied with a circulation field in the lower layer of clouds. A two-dimensional, time-dependent and warm cumulus cloud model has been used to investigate problems concerning cloud merger and interaction. The results of numerical merger show: (i) Two clouds formed at the same time have influence on each other at a shorter time on one hand, it is possible that they merge with equal intensity, and on the other, it is impossible that they merge with unequal intensity; in case of quite different intensities the weak cloud is depressed and the strong cloud accretes. (ⅱ (Ⅲ) The merged cloud develops more violently than the unmerged and produces more rainfall. (Ⅳ) Cloud merger results from the action of a horizontal pressure gradient accompanied with a circulation in the lower layer of clouds.