With regards to the assembly line of cost control of Dechang (HK) company, the motor housing’s cost control of process will be necessarily respected. Because the supply quantity is big in a machine the price of motor housing is small, so that the cost control of automatic production line is significant with modeling. It is found that the control of equipment includes in shaft and crank linkage for benefit which also needs to be controlled in detail. For the sake of benefits can we fundamentally resolve the main problem of high cost process.