The effect of optical current transformer (OCT) output voltage for linear birefringence is analyzed, it's incompleteness problem of the examination of output light's information in the difference divided by addition detection system is pointed out, linear birefringence in bulk-glass optical current sensing head cannot be examined separately by the difference divided by addition examination system, it's proved and concluded theoretically by Jones matrix. Bringing forward the elliptical-polarization detection system of OCT, the formula to explain the relationship among the thermal induced linear birefringence, Faraday rotation angle, output elliptically polarized light's ellipticity and obliquity are deduced which are based on the elliptically polarized light parameter formula. The elliptically polarization examination system's completeness for the examination of output light's information is proved, and the thermal induced linear birefringence and electrical current intensity can be tested in the same time. The output of the 3-state detection, horizontal, vertical and 45° 3 polarization state testing are brought forward for ensuring being in real time. Linear birefringence's effect is conquered and electrical current intensity can be tested in real time, the thermal-induced linear birefringence's effect on optical current transformer is solved theoretically.