The invention discloses a pneumatic safety device comprising a mechanically-controlled two position three-way valve and a pneumatically-controlled two position three-way valve; the mechanically-controlled two position three-way valve comprises an air inlet, an air outlet and a control valve rod; the pneumatically-controlled two position three-way valve comprises an air inlet, an air outlet and a control opening; and the air outlet of the mechanically-controlled two position three-way valve is communicated with the control opening of the pneumatically-controlled two position three-way valve. When the pneumatic safety device is in working, the control valve rod of the mechanically-controlled two position three-way valve is in transmission connection with a fault part, the air outlet of the mechanically-controlled two position three-way valve is communicated with the control opening of the pneumatically-controlled two position three-way valve, and the air outlet of the pneumatically-controlled two position three-way valve is communicated with an air inlet of an effected part, thus, the mechanical movement of the fault part can control whether the air outlet of the mechanically-controlled two position three-way valve gets air or not through the control valve rod, and then control whether the air outlet of the pneumatically-controlled two position three-way valve gets air or not and control whether the air inlet of the effected part gets air or not, and finally, a linkage relationship is established between the mechanical movement of the fault part and the normal movement of the effected part.