The electrical source is commonly supplied by electronic facilities,the security and reliability of which is to a large extent based on the circuit protection from their switches.By an incomplete statistics,eight percent of the security and reliability problems of electronic facilities result from the design of circuits.This article points out the existing shortcomings in the electrical circuit and comes to a conclusion of the basic unites for the security protecting circuit by means of further analysis on the circuit protection of surge current,over-carried voltage,lower-carried voltage and over-carried current protection in the switch electrical source.