The new polarizers with grooved mirrors were installed in ECRH system on the GAMMA 10 to get the optimal polarized wave. Numeric calculation and low power performance test of this pair of polarizers was agreed well. And it is found that the setting error of polarizer angle within ±5° gives negligible reduction of the X-mode ratio less than 1%. On the experiment in the GAMMA 10, it is shown that the fraction of X-mode has key role to heat plasma efficiently.