The invention discloses an intelligent optimization and monitoring device used for a direct-current charger and a direct-current charging system. According to a monitored battery charging request message BCL, needed power P0 of an electric car is calculated; a rounding function is adopted to round up to an integer, and the number N of charging sub modules currently required to be put into operation is obtained; a corresponding charging sub module input number message instruction is generated and sent to a charging controller; the current output efficiency eta is calculated; the N is adjusted,the current load rate lambda is calculated, when the current load rate lambda is within the preset range, the input number message instruction is generated, and is sent to the charging controller, andthe current output efficiency eta is calculated; N is continuously adjusted until when the N is adjusted up or down, lambda exceeds the preset range; and the maximum output efficiency eta max and theoptimal input number are output, and the optimal charging running state is executed. Optimization of the output efficiency of the direct-current charger can be achieved, and on the basis, the electric larceny analysis in the charging process can be achieved.