Principle of maximum power point tracking（ MPPT） is discussed in detail. Aiming at problem of power loss caused by fixed step of perturbation and observation（ P＆O） method

a strategy of variable step length is proposed. Arctan function is used to normalized step length

which makes the step length the variable in certain range and simulation verification is carried out

the maximum power point tracking platform of solar energy is designed. Including hardware and software design. The hardware includes Boost boosting circuit

drive circuit and sampling circuit. Algorithm partially uses impoved normalized variable step size P＆O method

the code based on TMS320 F28335 is developed. The experimental result can track the maximum power point accurately

verify feasibility of the system.