The structure，martensitic transformation and magnetism have been studied in the CoNiGa alloys after certain Ga substrated by Si. From the experimental results，we found that the alloy can form pure body-centered cubic structure accompanied by good thermal martensitic transformation when the atom ratio of Si lies in the range 0—10%. It can be concluded from further analysis that it is not only the radius of the doped atom but also the radius ratio of the doped atom and the host atom that affect the stability of the austenite. At the same time，it can be found that the Curie temperature and the saturated magnetization decrease with increasing Si. But the anisotropy of the martensite increases with the increasing Si，which is of significance for obtaining large magnetically-induced-strain.