Earlier intervention for pulmonary hypertension (PH) has been reported to improve the prognosis of patients with connective tissue disease (CTD). However, it is not fully elucidated how rapidly PH develops in patients showing normal mean pulmonary arterial pressure (mPAP) at the index investigation. We evaluated 191 CTD patients with normal mPAP retrospectively. The mPAP was estimated by the formerly defined method employing echocardiography (mPAP^echo). We investigated predictive factors that predict increasing mPAP^echo at follow-up transthoracic echocardiography (TTE) using uni- and multi variable analysis. The mean age was 61.5 years old, and 160 patients were female. The percentage of patients in whom mPAP^echo exceeded 20 mmHg at follow-up TTE was 38%. Multivariable analysis revealed that acceleration time/ejection time (AcT/ET) measured at the right ventricular outflow tract at initial TTE was independently associated with the consequent increase of mPAP^echo at the follow-up TTE. When using 0.43 of best cutoff value in AcT/ET calculated by receiver operating characteristic analysis, the change in mPAP^echo in patients with low AcT/ET was significantly higher than in those with high AcT/ET (3.05 mmHg in patients with AcT/ET < 0.43 and 1.00 mmHg in patients with AcT/ET ≥ 0.43, p < 0.001). Thirty-eight percent of CTD patients who show the normal estimated mPAP by TTE develop gradual elevation of mPAP to the level to consider early intervention within 2 years. AcT/ET at initial TTE can predict increasing mPAP at follow-up TTE.