The invention relates to the field of power system analysis, in particular to a power transmission and transformation system health degree evaluation method capable of considering season condition changes. The method comprises the following steps that: (S1): according to different power grid operation state constrain conditions, dividing a system state into three states including health (H), sub-health (M) and risk (R); (S2): carrying out fault rate seasonal statistics; (S3): considering a characteristic that a fault rate changes along with seasons, and deducing the situation method of the inhomogeous Poisson process operation state of the periodic intensity of a power transmission and transformation component, wherein the simulation method is that seasonal fault rate inhomogeous simulation is added into a sequential Monte Carlo total calculation step, and the simulation result is a probability of each operation state of the system under a well-being theoretical framework. By use of the method, according to season alternating changes, the power transmission and transformation system health degree is evaluated, and an evaluation result can more truly reflect the health degree level of the power transmission and transformation system under the drastic change of seasons so as to improve planning and investment benefits.