public static class PredicateBuilder
    {
        public static Expression<Func<T, bool>> True<T>() { return f => true; }
        public static Expression<Func<T, bool>> False<T>() { return f => false; }

        public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1, Expression<Func<T, bool>> expr2)
        {
            var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
            return Expression.Lambda<Func<T, bool>>
                  (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
        }

        public static Predicate<T> ConvertToPredicate<T>(this Func<T, bool> func)
        {
            return new Predicate<T>(func);
        }
    }

    var pre = PredicateBuilder.False<Item>();

            foreach (var cd in catalogs)
            {
                var cataPre = PredicateBuilder.True<Item>();
                if (!string.IsNullOrWhiteSpace(cd.BrandCd))
                {
                    cataPre = cataPre.And((item) => item.BrandCd == cd.BrandCd);
                }
                if (!string.IsNullOrWhiteSpace(cd.NameCd))
                {
                    cataPre = cataPre.And((item) => item.NameCd == cd.NameCd);
                }
                pre = pre.Or(cataPre);
            }
//true拼接and,false拼接or