The invention discloses an improved control method for variable-step-length maximum power point tracking on the basis of beta parameter. The improved control method comprises the following steps: sampling voltage and current output by a photovoltaic module, thus obtaining a sampling voltage value V(k) and a sampling current value I(k), and then calculating an instantaneous value betaa of beta; defining the value range of beta according to the range of temperature and illumination, wherein a minimum value is betamin, the maximum value is betamax, and if betaa is more than or equal to betamin and less than or equal to betamax, the tracking step length is a fixed step length; if betaa is more than betamax, adjusting the step length, and adopting smaller proportionality coefficient value N1, wherein the step length deltaD is equal to N1 multiplied by (betaa-betag), betag is a reference value, and an intermediate value between betamax and betamin is taken; if betaa is less than betamin, adjusting the step length, and adopting larger proportionality coefficient value N2, wherein the step length deltaD is equal to N2 multiplied by (betaa-betag). The improved control method disclosed by the invention has the advantages that two kinds of different proportionality coefficients N are adopted for rising and falling of illumination, so that fast dynamic tracking is realized and the phenomenon of misjudgment is avoided.