This　paper　presents　a　subspace　identification　method　for　closed-loop　systems　with　unknown　deterministic　disturbances.　To　deal　with　the　unknown　deterministic　disturbances,　two　strategies　are　implemented　to　construct　the　row　space　that　can　be　used　to　approximately　represent　the　unknown　deterministic　disturbances　using　the　trigonometric　functions　or　Bernstein　polynomials　depending　on　whether　the　disturbance　frequencies　are　known.　For　closed-loop　identification,　CCF-N4SID　is　extended　to　the　case　with　unknown　deterministic　disturbances　using　the　oblique　projection.　In　addition,　a　proper　Bernstein　polynomial　order　can　be　determined　using　the　Akaike　information　criterion　(AIC)　or　the　Bayesian　information　criterion　(BIC).　Numerical　simulation　results　demonstrate　the　effectiveness　of　the　proposed　identification　method　for　both　periodic　and　aperiodic　deterministic　disturbances.　IEEE