The miniaturization of oven-controlled crystal oscillators (OCXO) is necessary for developing communication technology. When developing a small-sized OCXO, we found that frequency curves of the OCXO leaned upwards uniformly when ambient temperature increased from -40 to 85 ℃, failing to satisfy the requirement of ±3×10-9. Variations in the heating current of the oscillator with temperature cause biasing voltage fluctuations in the variable diode when current flows through the ground pin made of metal with low conductivity. This problem was solved using the proposed dual ground pin and passive compensation methods.