Abstract: The motor transport is economical in opencast in early period due to short distance，but becomes costly with the distance increasing.The initial investment of Auto-belt-dumping plough combined transport process is high but its operating cost is low.So it is the best transport mode instead of motor transport in the late period of mining.The occasion of adopting the combined transport plays an important rule in improving its economic advantage.It is the key link to find the reasonable transition point from motor transport to combined transport.Through decomposing operating costs of two transports item by item，a mathematical model of the operating costs is built based on the relevant factors to obtain the operation costs of each transport per unit by simulating a mine.Large sets of data processing is completed with the aid of excel.Through analyzing and comparing the calculated results，a reasonable and optimal transition point from motor transport to combined transport was determined as the fifth year.In this moment，the advantages of two transports could be complemented with each other to minimize the operating costs

Key words: Motor transport, Combined transport, Continuous transport, Economical transport distance