When electric tractor working on heavy load model, such as plowing and rotary tillage, the peak power with high frequency of the working condition has more randomness. Energy systems of the electric tractor, which consists of single type of electric power source, e.g. batteries, may not effectively match the required power of dynamic load characteristic. Aimed at these problems, the electric tractor energy system and the management strategy were researched by the way based on the power spectral density of tractor load. By the analyses of electric drive train power flow, power spectral density of potential flow variables of tractor load and frequency characteristic in discharge process of common electric source, the feasibility of the way to separate the power flows with low frequency and high frequency via synergic electric power supply system was discussed. By mathematically building the constraint modelling of the endurance performance, power property, maximum using weight of tractor, steady and dynamic characteristic of load, the design method of energy systems with synergic electric power supply system in electric tractor was proposed. After that, the 18.5kW electric tractor energy system which was assembled by the parallel connection between batteries and super capacitors via DC-DC converter was designed. For the elimination of peak power with high frequency of battery and the direction control of the super capacitor power flow, the double DC-DC converter control strategy based on logic control was generated. For the requirement of time-frequency analysis, the power distribution controller of the management strategy was designed by using two-channel filter bank with Haar wavelet. By constructing the mutual spectral density function between Gaussian white noise and working load of the tractor on plowing and rotary tillage, the load-time wave used in the simulation was established. The simulation ran on the platform that the simulation model of tractor plowing and rotary tillage unit built on AVL CRUISE dynamically combined with the management strategy simulation model on Matlab/Simulink. And it can be found that the management strategy based on power spectral density can limit the frequency of the power flow transiting electric power the batteries of synergic electric power supply system on the fundamental frequency of working load. Under the plowing condition, the frequency of battery electric power was cut off at 2Hz. And under the rotary tillage condition, the frequency of battery electric power was cut off at 7Hz. The amplitudes of electric power flow conformed to positive skew distribution. The remainder of required power was provided by super capacitance. And the amplitudes of remaining electric power flow accorded with standard normal distribution. The research proposed can offer theory reference and technology support to other researchers whose working field would be related to electric tractor and energy management.