To calibrate an electric field prove for evaluating specific absorption rate (SAR) of wireless devices operated in the MHz band, we have proposed the use of circular loop antenna immersed in tissue-equivalent liquid. In our proposed method, near-field gain of the loop antenna should be evaluated to estimate the fields radiated by the loop antenna. However, there is a serious problem that its size which can determined as the near-field gain is constant in its neighborhood is much larger than a liquid container as the frequency is lower, for example, at 6.78MHz. In this paper, we focus on estimating antenna factor for transmitting loop antenna and we examine that the distance property of the small circular loop antenna in the liquid can be estimated in its neighborhood with the antenna factor for transmitting loop antenna by using the method of moments.