The paper establishes switching optimal model of distribution system based on LCC. To seek optimal economy under multi-constrained conditions, it contains original investment cost, operation and maintenance cost, outage loss cost and disposal cost. An improved BDE is put up to solve the above model. It uses normal cloud generator to optimize individual cross factor which has stability and randomness. The model and algorithm are applied to IEEE-RBTS system; the result proves that the model meets the actual circs better, and IBDE greatly improves global search probability with slightly low convergence speed, but has faster speed than GA algorithm.