A circuit for protecting data information of an electronic equipment, comprising a processor and an electronic device connected with the processor via a signal line, wherein said circuit for protecting data information further comprises a capacitance detection module electrically connected with the signal line, the capacitance detection module having a detecting end connected with the signal line and a pulse output end connected with the processor; wherein when performing power-on detection on the electronic equipment for the first time, a pulse signal formed by the stray capacitance of the signal line together with the capacitance detection module is transmitted to the processor, and then the frequency of the pulse signal is recorded as a standard frequency by the processor; wherein during use of the electronic equipment, the processor compares a received real-time frequency with the standard frequency and makes a judgment that there is outside foreign matter contacting with the signal line if there is a difference between the real-time frequency and the standard frequency exceeding a preset value, wherein the stray capacitance of the signal line is changed and the pulse signal formed by the capacitance detection module combining the stray capacitance is also changed and the processor erases significant data in the electronic equipment; wherein the signal line is a connecting wire connecting the electronic device and the processor, wherein the capacitance detection module is a RC oscillating circuit comprising a first inverter (U418A); the number of the signal lines is more than one; and a multiplexer is provided between the signal lines and the capacitance detection module, wherein the multiplexer is an analog 8-channel multiplexer which has eight input ends connected with the signal lines, one output end connected with the capacitance detection module and three control input ends connected with the processor, and the analog 8-channel multiplexer determines which one of the input ends to communicate with the output end according to a composite signal from the three control input ends; when performing power-on for the first time, the processor sends eight composite signals to the analog 8-channel multiplexer one by one, and records a pulse frequency produced by the capacitance detection module together with the signal line relative to each composite signal as a standard frequency relative to the composite signal; wherein during use, the processor sends out the composite signals and compares the received real-time frequency with the standard frequency relative to the composite signal, and the processor will make a judgment that there is outside foreign matter contacting with the signal line relative to the composite signal if there is a difference between the real-time frequency and the standard frequency relative to the composite signal exceeding a preset value, the stray capacitance of the signal line is changed and the pulse signal formed by the capacitance detection module combining the stray capacitance is also changed and the processor sends out an alarm signal and/or a signal for protecting the significant data; wherein the electronic equipment is a POS machine, an ATM machine or a cash register; and the electronic device comprises a keypad, a display screen, an IC card reader, and a magcard reader; wherein said detecting end of said capacitance detection module is connected to an input of said first inverter (U418A) via a first capacitor of said capacitance detection module.