yes, since when you ground the pin through your switch, it brings the pin from its floating state down to ground or about 0volts. You could wire the A0 pin through a weak pullup resistor to the 3V3 pin; essentially fixing its state to 3.3V.
analogRead() in that state would return approx 4095, the highest 12bit value. Then when you short it to ground by closing your switch,
analogRead() should return a value towards zero.
But since you are using a binary device, try using
const int sensorPin = D6;
const int ledPin = D7;
pinMode(sensorPin, INPUT_PULLUP); // set pin as an input and pullup to 3.3V using internal pullup resistor
pinMode(ledPin, OUTPUT); // set on-board led to output
the reed switch would be wired across D6 and GND in this example