The invention relates to a passive smart lock system based on limited interaction. The passive smart lock system based on limited interaction comprises a smart lock base station and a smart key, wherein the smart lock base station is arranged on a door and comprises a base station master control module, a trigger module, a low-frequency transmitting module and a low-frequency transmitting antenna, a high-frequency receiving module, a high-frequency receiving antenna, a motor driving module and an auxiliary signal transmitting module, the smart key comprises a key master control module, a low-frequency receiving module, a low-frequency receiving antenna, a high-frequency transmitting module and a transmitting antenna, the transmitting direction and the transmitting zone of the auxiliary signal transmitting module is outside a door, the smart key also comprises an auxiliary signal receiving module used for monitoring whether the current zone has an auxiliary signal and an auxiliary condition judgment module for judging the current key position and selectively judging whether to meet the current ID transmitting condition according to a condition whether the auxiliary signal exists, and the auxiliary condition judgment module is connected with the key master control module. The passive smart lock system based on limited interaction can effectively distinguish whether the key is positioned inside the door or outside the door, and has good safety.