The invention discloses an energy managing method and system based on a building photovoltaic micro-grid. Operation historical data of a building photovoltaic generating system and homochronous weather condition information are obtained, and a building photovoltaic generating power prediction model is established based on the operation historical data of the building photovoltaic generating system and the homochronous weather condition information; electrical load historical data and homochronous environment monitoring information in a building are obtained, and a building load demand predicting model is established based on the electrical load historical data and the homochronous environment monitoring information; according to the demand application of electric vehicles managed in the building, the traffic dispatching plan of the electric vehicles is formulated in advance, and the electrical charge state when the electric vehicles are driven away from the building every time and the electrical charge state when the electric vehicles are driven back to the building are estimated; a target function of the whole building photovoltaic micro-grid is established according to the building photovoltaic generating power prediction model, the building load demand predicting model and the traffic dispatching plan of the electric vehicles, and the charging and discharging power at every time frame when the electric vehicles park at the building is planned in advance through the optimization algorithm. The charging and the discharging power to the power grid from the electric vehicles parking at the building is controlled, and therefore the reliable power supply for the building electrical load is achieved, and the utilization ratio of building energy consumption is increased.