A characteristic signature of the string gas cosmology is to predict primordial power spectra with a red scalar but a blue tensor tilt.Nevertheless,this feature can also be realized in the so-called G-inflation model,in which the Horndeski operators have been introduced,where a blue tilt is realized by softly breaking the null energy condition.In this article we search for potential observational differences between these two cosmologies by performing detailed perturbation analyses based on the effective field theory approach.Our results show that,although both two models may produce blue tilted tensor perturbations,they behave differently on three aspects.Firstly,the string gas cosmology explicitly predicts a specific consistency relation between the index of the scalar modes ns and that of tensor ones nt,which can hardly be reproduced by G-inflation.Secondly,the string gas cosmology typically predicts invisible nonlinear fluctuations while G-inflation gives rise to observationally large non-Gaussianitiesas its kinetic term becomes important during inflation.However,after finely tuning the model parameters of G-inflation,there could remain a degeneracy between two models.Nevertheless,this degeneracy can be broken by the third aspect,that is,the scale dependence of the nonlinearity parameter,which is vanishing for G-inflation but blue tilt for the string gas cosmology.Therefore,we conclude that the string gas cosmology is in principle observationally distinguishable from the single field inflationary cosmology including G-inflation.