Abstract: The formation of orography induced convections and precipitation over a two dimensional small-scale two-ridge mountain in the conditionally unstable atmosphere depended mainly upon the upstream flow, the height of the two ridges and the width between them. There are two configurations for two-ridge orography considered, with a higher ridge in either the upstream or downstream of basic flow. For the case of the higher ridge located in the upstream, the formation and propagation of convection and/or precipitation over the mountain are mainly determined by the effect of the higher ridge, whose features are similar to that the single-ridge orography. For the case of the higher ridge located in the downstream, the upstream ridge could change the basic flow for the downstream ridge, and the interaction with the perturbation induced by the two-ridge orography, which results in the different regimes of convection and/or precipitation over the mountain. The width of valley primarily influences the discrepancies for the convection and/or precipitation over mountain between single and two-ridge orography. For the narrow valleys, the two ridge orography may be approximated by an envelope orography, so that the regimes of convection and/or precipitation are analogous to that of the single-ridge orography. For the wide valleys, the interactions between the flows over two different ridges are trivial, and then each ridge may be treated as the single-ridge orography. When the valley width lies in a certain range, however, the regimes for convection and/or precipitation are quite different from that for the single-ridge case. Four types of precipitation distribution are detected for the higher ridge located in the downstream with a moderate valley width: (1) precipitation located in the valley and in the upslope of the lower ridge; (2) precipitation located in the upslope of the higher ridge; (3) precipitation located in the peak of lower ridge and in the upslope of the higher ridge; and (4) quasi-stationary precipitation located in the peaks of two ridges and in the lee-side of lower ridge.