Abstract: In accordance with the statistics,an efficient log sorting line may be consisted of 1—6 conveyors,of which the log sorting line with one conveyor accounts to 31 per cent,two conveyors 34.6 per cent and three convyors 21.9 per cent.Owing to lack scientific basis in practice,the length distribution of tandem conveyors in one sorting line is very complicated.This paper theoretically probes into the reasonable length distribution of some tandem conveyors and gives the calculating method. In order to discuss the length distribution of conveyors,the variational law of the occupied coefficient by logs in the sorting line should be studied.In accordance with the factfinding data,this paper gives the formula (1) for calculating the occupied coefficient (?) in any section of the sorting line expressed by the ratio α of the length distribution The principle for determining the length distribution is that the maximum chain pull of each conveyor should be equal.Thus,this paper gives the formula (14) for calculating the ratio (α₁)₂ of length distribution of the first conveyor in two tandem conveyors sorting line and the formula (23) for calculating the ratio (α₁)_n of the first conveyor in n conveyorsorting line.In the last part,the author of this paper gives the optimum seeking method for determining the type of conveyor,the size of chain and the length of tandem conveyors under the given length L of the log sorting line.