The invention provides a photovoltaic inverter control parameter subsynchronous stability region control method and a controller. The method comprises steps: a complex frequency domain transfer function G(s) is built according to the mathematical model of a photovoltaic power generation system; based on the transfer function, a characteristic polynomial delta(s, kp, ki) is defined, and the control parameters kp and ki of the PI controller in the characteristic polynomial simultaneously appear in an odd number-th power term and an even number-th power term of the s; based on the transfer function and the characteristic polynomial, a test polynomial v(s) is defined, and in the test polynomial, kp and ki are separated in the odd number-th power term and the even number-th power term of the s; and Fourier transform is carried out on the test polynomial v(s), kp appears in an imaginary part polynomial q(omega, kp), ki appears in a real part polynomial p(omega, ki), the kp range is determined through the q(omega, kp), and according to each fixed kp value, a ki value which enables p(omega, ki) to be larger than 0 is determined.