The visiting premier and Prime Minister Yingluck Shinawatra also promised to propel bilateral trade to US$100 billion by 2015 from about $70 billion this year.
Mr Li was the first foreign dignitary to address parliament in its 81-year-old history and the visitor did not waste the opportunity to seek support for Chinese participation in infrastructure schemes in the kingdom.
"We hope the parliamentarians will vote for China," he told the joint parliamentary session in his 30-minute speech, citing close Sino-Thai relations.
The high-speed rail project is part of the 2-trillion-baht infrastructure improvement programme for which the government is seeking parliamentary approval. The scheme mainly focuses on railway development and the construction of four lines of high-speed rail lines, one of them linking Bangkok to Nong Khai.
China is one of the countries the government is courting to invest in the northeastern line as it could connect another line planned from the Chinese border to Vientiane, the capital of Laos.
On the tourism front, with Japan's decision to end visa requirements for Thais in July, the attention has shifted to China.
Mr Li was also keen on holding talks with Thailand to exempt visas for the two countries' citizens, Xinhua reported.
"There is an old Chinese saying that goes: the more exchanges among relatives, the warmer their relations will become," the Chinese official news agency quoted him as saying.
The two issues were tabled in talks between the two prime ministers, who witnessed their ministers signing six documents.
The focus was on a memorandum of understanding to barter Thai agricultural products for Chinese infrastructure investments in Thailand.
Transport Minister Chadchart Sittipunt has said the agreement would involve rice and rubber products as partial payments for Chinese goods and services related to high-speed rail ventures. However, he cautioned that details needed to be worked out later and more bidders would be called in order to promote transparency.
Thailand and China will further discuss a plan on visa exemptions to promote trade and tourism, Government House said in a statement released after the meeting.
Last year, 2.78 million Chinese tourists came to Thailand, a 12% increase from a year earlier, according to the Tourism Department. Visitors from China jumped to 3.2 million in the first eight months of this year.
China is one of the favourite destinations for Thai tourists.
Mr Li on Saturday is to travel to Chiang Mai, Ms Yingluck's hometown, and then leave for Vietnam on Sunday.