Nowadays, due to the lack of fresh water resources in the world, water desalination has become one of the important fields of technology. Water desalination by humidification-dehumidification method is one of the thermal methods of water desalination which has attracted the attention of researchers due to its less sedimentation and high flexibility feed quality. Hence, determining the efficiency of this type of water desalination system provides researchers with a suitable perspective to investigate the capability of this type of system. In this research, first, we have investigated a system with a finite size, the effect of the temperature of the water entering the humidifier and the ratio of the mass flow rate of salt water to the mass flow rate of air on the Gained Output Ratio (GOR) of the system were studied. Then, we determined the optimal value of this ratio at a certain temperature that has maximum GOR. Also, the thermodynamic balance of a system with a finite size and a finite number of mass extractions and injections was investigated in which we examined the effect of enthalpy pinch and the number of mass extractions and injections on the GOR of the system. It was also found that in low enthalpy pinches, the GOR of the system is maximum, by increasing the number of mass extractions and injections, But with the increase of pinch enthalpy, the effect of the number of extractions on the GOR decreases. So that in the pinch enthalpy of more than 20, the difference between the GOR without extraction and 8 extractions is less than 10%. Also, in this research, the effect of salt concentration on the effect of the number of mass extractions and injections on the maximum GOR of the system has been investigated. Only in the case where the water salinity is zero, infinite extraction leads to infinite GOR. But for each specific salinity, there is a maximum GOR value that the system GOR will reach if the number of extractions increases. This value decreases with the inc