Within the framework of non-extensive statistical mechanics, statistical distributions and thermodynamic formulas for a completely open system have been derived on the basis of Shannon entropy using the maximum entropy method, and an ideal Boson system and the corresponding linear filament system have been discussed. For the ideal Boson system, the thermodynamic properties calculated here are the same as those calculated using the grand canonical distribution, only with the average volume replacing the constant volume in the grand canonical distribution. For the linear filament system, the thermodynamic properties calculated here are the same as those calculated for the E-V distribution, only with the average number of units replacing the constant number of units in the E-V distribution. However, the relative fluctuations calculated in the ideal Boson system are greater for the completely open system than for the grand canonical system. This is a completely new result, with which it is possible to explain some phenomena that cannot be explained by B-G statistical mechanics, such as the critical phenomenon.