The invention discloses a monitoring method and system based on a smart phone. The monitoring method comprises the steps that a monitoring function is started on the smart phone, the smart phone then sends camera starting signals to a mobile phone companion device through Bluetooth; an own camera is started on the mobile phone companion device and starts to capture images in a monitoring area; the smart phone judges whether WIFI starting signals are received or not, an own WIFI module is started on the smart phone if the WIFI starting signals are received, and meanwhile the WIFI starting signals are sent to the mobile phone companion device through the Bluetooth; an own WIFI module is started on the mobile phone companion device, and meanwhile the captured images are processed and then sent to the smart phone through the WIFI; the smart phone receives the image information from the mobile phone companion device through the WIFI, and the image information is stored and/or displayed after being processed. Through the implementation of the technical scheme, cost is saved. In addition, due to the fact that the image information is transmitted through the WIFI while control information is transmitted through the Bluetooth, energy consumption can be lowered, and interference resisting capability is strong.