After graduating from Cooper Union in 1969 and her return to Hong Kong, Zhao Hai Tien set up her first studio in an old colonial house on Broadwood Road in Happy Valley. Her early works from this period include a series of three-dimensional works heavily inspired by the hard-edge abstraction of minimalism and environmental art. Influenced in part by her father's architecture career, her works maintained a foundation in the living environment. She used an unconventional medium, an automotive spray gun, to paint wooden folding screens, creating a series of conceptual environmental artworks. Construction C (1971) was a large-scale installation in Minden Plaza shopping mall in Causeway Bay, for which Hai Tien sprayed acrylic on hard film. This work showcased her ability to create large-scale public installations rooted in minimalist concepts.

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Following her marriage in 1973, Hai Tien travelled with her husband to Europe, Australia, the US and throughout Southeast Asia, which broadened her understanding of different cultures and forms of art. Untitled (1970) and Inner Light (1972) are representative works from this period that are dominated by gradients of single colours and simple geometric shapes. Despite the conceptual influence of Frank Stella's shaped canvases, Hai Tien focused on simplifying her works, the individuality of space and the visual experience of her environmental art.​

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Into the boundless universe,

The infinite space

The endless time

Man is thrust with his limited life.

—Hai Tien, 1973

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1969 年趙海天於紐約庫柏聯盟學院畢業後返回香港，在跑馬地樂活道一棟殖民時期建築的一間房裡設立第一個工作室。這時期的早期作品包括一系列深受極簡主義硬邊抽象畫和環境藝術影響的立體作品。受其父建築師職業的影響，她的創作始終基於生活環境。她用的媒材很特殊――在折疊木板上用噴槍噴漆作畫，創作一系列概念性的環境藝術作品。《建築 C》（1971）是她在銅鑼灣名店街商場（Minden  Plaza）創作的大型裝置作品。她用塑膠彩顏料在硬膠片上噴繪。這件作品展現其創作植根於極簡主義理念的大型公共裝置的功力。

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1973 年婚後，趙海天與丈夫遊歷歐洲、澳洲、美國和東南亞各地，拓寬對多元文化和不同藝術形式的理解。《無題（無限與有限）》（1970）和《心光》（1972）是這時期的代表作，構圖以單一色彩的漸變和簡潔的幾何形狀為主。儘管受美國畫家法蘭克．史帖拉異形畫布概念的影響，海天仍專注於簡化作品，突顯環境藝術創作中獨特的空間和視覺體驗。

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身處無垠宇宙，

空間無限

時間無盡

人類被有限生命所裹挾。

——趙海天（1973年）

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