It was confirmed that the parental broiler breeders were infected with Mycoplasma gallisepticum（MG）in a large farm when they were at about 44 weeks old. In order to evaluate the treatment effect of relevant sensitive drugs，the minimal inhibitory concentration（MIC）of the MG strain isolated from the farm was determined，Enrofloxacin and Tiamulin were respectively used for comparative treatment，then the infection rate was calculated according to the status of MG infection in hatching eggs or dead embryos at late hatching stage after one course of treatment by nested PCR. It was shown that，by MIC determination，for the drugs with MIC≤5 μg/mL，the sensitivity of Vorimillin，Doxycycline，Temicin，Enrofloxacin，Spectinomycin，Tylosin and Florfenicol was successively decreasing. After comparative treatment，it was shown that MG infection in hatching eggs could not be completely cleaned up by the two drugs，but its spreading could be reduced，and its infection rate decreased significantly（P=0.006，＜0.01）compared with the untreated control group；after one course of treatment by the two drugs，the infection rates of unhatched eggs and dead embryos at late hatching stage had no significant difference（P=0.391，＞0.05），indicating similar effect of the two drugs. It was concluded that the sensitive drugs that could prevent or reduce the spreading of MG via eggs were rapidly selected through calculating the infection rate of hatching eggs or dead embryos by nested PCR，so as to evaluate the treatment effect of various antibiotics. Some references were hereby provided to establish an evaluation model for MG infection and control effect.