Fault-injection, as a perfected technique for software testing, now has been put into practical use. However, only a very few of the documents have expounded on how to use fault-injection technique in soft ware black-box testing. A new approach to the difficulty, i.e., peripherally in jecting faults in the software is presented in this paper. By means of a fault- imbedded environmental simulation, faults are injected in the input level of the software under test. These faults may induce inherent failure mode, thus bringi ng about unexpected output--consequently, the anticipated goal of the test is attained. This method has been used for testing railway signaling control system software and desirable results have been achieved.