The timely and accurate identification of estrus in dairy cows is an important basis for improving the success rate of artificial insemination and conception rate. Artificial estrus monitoring of dairy cows is time-consuming and laborious, and activity and non-contact video monitoring cannot achieve calm estrus early warning. To solve these problems, based on the physiological changes of vaginal mucus during estrus in dairy cows, an estrus monitoring scheme for dairy cows was proposed based on the changes of vaginal resistance. An implantable resistance sensor for dairy cow vagina was designed to collect the value of vaginal resistance, which consisted of a brass resistance probe and an 8-claw anti-skid device. The wireless transmission system was developed with the help of 2.4GHz ZigBee network, which transmitted the vaginal resistance value to the coordinator node wirelessly, and the coordinator was transmitted to the monitoring center via RS485 bus. A real-time monitoring system for vaginal resistance of dairy cows was developed, which realized the accurate collection and remote real-time monitoring of vaginal resistance of dairy cows. The accuracy, stability, reliability and energy availability of the implantable resistance sensor and monitoring system were tested respectively. The results showed that the implanted resistance sensor was easy to install and light in weight, and could measure resistance in the range of 1~1000Ω. The measurement accuracy was less than ±2% and the maximum fluctuation of resistance in 24h was 2Ω. In a 450m2 dairy farming area, the success rate of ZigBee network data transmission was not less than 98.5%. The implantable sensor terminal node could work continuously for 38d with 7.4V/6500mA·h lithium battery energy supply. The monitoring system ran stably and could monitor the change of vaginal resistance of dairy cows accurately, reliably and in real time. The research can provide a new method for accurate prediction of estrus degree and ovulation time of dairy cows, and also provide reference for estrus detection of other animals.