Gan-Gurevich constructed a CAP form on the split exceptional group G_2 using theta correspondence. We show that their form is a quaternionic cusp form in the sense of Gan-Gross-Savin in level one case. In higher levels, we need Arthur's multiplicity formula. The weight k form is a lift from an elliptic newform of weight 2k. We call it Gan-Gurevich lift. By using the degenerate Whittaker functions, we can give explicit Fourier expansion of the lift. Our results give a partial answer to Gross' conjecture. This is a joint work with Takuya Yamauchi.